Microsoft Csg1 [Read Only] Oracle Database 11g SQL Fundamentals I Volume Student Guide
D59980-Oracle-SQL-Fundamentals-Student-Guide-Volume-1-I
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Oracle Database 11g: SQL
Fundamentals I
Volume I • Student Guide
D49996GC11
Edition 1.1
April 2009
D59980
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Authors
Copyright © 2009, Oracle. All rights reserved.
Puja Singh
Brian Pottle
Disclaimer
Technical Contributors
and Reviewers
Claire Bennett
Tom Best
Purjanti Chang
Ken Cooper
László Czinkóczki
Burt Demchick
Mark Fleming
Gerlinde Frenzen
Nancy Greenberg
Chaitanya Koratamaddi
Wendy Lo
Timothy Mcglue
Alan Paulson
Bryan Roberts
Abhishek Singh
Lori Tritz
Michael Versaci
Lex van der Werff
This document contains proprietary information and is protected by copyright and
other intellectual property laws. You may copy and print this document solely for your
own use in an Oracle training course. The document may not be modified or altered in
any way. Except where your use constitutes "fair use" under copyright law, you may
not use, share, download, upload, copy, print, display, perform, reproduce, publish,
license, post, transmit, or distribute this document in whole or in part without the
express authorization of Oracle.
The information contained in this document is subject to change without notice. If you
find any problems in the document, please report them in writing to: Oracle University,
500 Oracle Parkway, Redwood Shores, California 94065 USA. This document is not
warranted to be error-free.
Restricted Rights Notice
If this documentation is delivered to the United States Government or anyone using
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applicable:
U.S. GOVERNMENT RIGHTS
The U.S. Government’s rights to use, modify, reproduce, release, perform, display, or
disclose these training materials are restricted by the terms of the applicable Oracle
license agreement and/or the applicable U.S. Government contract.
Trademark Notice
Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other
names may be trademarks of their respective owners.
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Editors
Raj Kumar
Amitha Narayan
Vijayalakshmi Narasimhan
Graphic Designer
Satish Bettegowda
Publishers
Sujatha Nagendra
Syed Ali
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Contents
Preface
I
Introduction
Lesson Objectives I-2
Lesson Agenda I-3
Course Objectives I-4
Course Agenda I-5
Appendixes Used in the Course I-7
Lesson Agenda I-8
Oracle Database 11g: Focus Areas I-9
Oracle Database 11g I-10
Oracle Fusion Middleware I-12
Oracle Enterprise Manager Grid Control 10g I-13
Oracle BI Publisher I-14
Lesson Agenda I-15
Relational and Object Relational Database Management Systems I-16
Data Storage on Different Media I-17
Relational Database Concept I-18
Definition of a Relational Database I-19
Data Models I-20
Entity Relationship Model I-21
Entity Relationship Modeling Conventions I-23
Relating Multiple Tables I-25
Relational Database Terminology I-27
Lesson Agenda I-29
Using SQL to Query Your Database I-30
SQL Statements I-31
Development Environments for SQL I-32
Lesson Agenda I-33
The Human Resources (HR) Schema I-34
Tables Used in the Course I-35
Lesson Agenda I-36
Oracle Database 11g Documentation I-37
Additional Resources I-38
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Summary I-39
Practice I: Overview I-40
1
Retrieving Data Using the SQL SELECT Statement
Objectives 1-2
Lesson Agenda 1-3
Capabilities of SQL SELECT Statements 1-4
Basic SELECT Statement 1-5
Selecting All Columns 1-6
Selecting Specific Columns 1-7
Writing SQL Statements 1-8
Column Heading Defaults 1-9
Lesson Agenda 1-10
Arithmetic Expressions 1-11
Using Arithmetic Operators 1-12
Operator Precedence 1-13
Defining a Null Value 1-14
Null Values in Arithmetic Expressions 1-15
Lesson Agenda 1-16
Defining a Column Alias 1-17
Using Column Aliases 1-18
Lesson Agenda 1-19
Concatenation Operator 1-20
Literal Character Strings 1-21
Using Literal Character Strings 1-22
Alternative Quote (q) Operator 1-23
Duplicate Rows 1-24
Lesson Agenda 1-25
Displaying the Table Structure 1-26
Using the DESCRIBE Command 1-27
Quiz 1-28
Summary 1-29
Practice 1: Overview 1-30
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Restricting and Sorting Data
Objectives 2-2
Lesson Agenda 2-3
Limiting Rows Using a Selection 2-4
Limiting the Rows That Are Selected 2-5
Using the WHERE Clause 2-6
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Character Strings and Dates 2-7
Comparison Operators 2-8
Using Comparison Operators 2-9
Range Conditions Using the BETWEEN Operator 2-10
Membership Condition Using the IN Operator 2-11
Pattern Matching Using the LIKE Operator 2-12
Combining Wildcard Characters 2-13
Using the NULL Conditions 2-14
Defining Conditions Using the Logical Operators 2-15
Using the AND Operator 2-16
Using the OR Operator 2-17
Using the NOT Operator 2-18
Lesson Agenda 2-19
Rules of Precedence 2-20
Lesson Agenda 2-22
Using the ORDER BY Clause 2-23
Sorting 2-24
Lesson Agenda 2-26
Substitution Variables 2-27
Using the Single-Ampersand Substitution Variable 2-29
Character and Date Values with Substitution Variables 2-31
Specifying Column Names, Expressions, and Text 2-32
Using the Double-Ampersand Substitution Variable 2-33
Lesson Agenda 2-34
Using the DEFINE Command 2-35
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Using the VERIFY Command 2-36
Quiz 2-37
Summary 2-38
Practice 2: Overview 2-39
3
Using Single-Row Functions to Customize Output
Objectives 3-2
Lesson Agenda 3-3
SQL Functions 3-4
Two Types of SQL Functions 3-5
Single-Row Functions 3-6
Lesson Agenda 3-8
Character Functions 3-9
Case-Conversion Functions 3-11
Using Case-Conversion Functions 3-12
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Character-Manipulation Functions 3-13
Using the Character-Manipulation Functions 3-14
Lesson Agenda 3-15
Number Functions 3-16
Using the ROUND Function 3-17
Using the TRUNC Function 3-18
Using the MOD Function 3-19
Lesson Agenda 3-20
Working with Dates 3-21
RR Date Format 3-22
Using the SYSDATE Function 3-24
Arithmetic with Dates 3-25
Using Arithmetic Operators with Dates 3-26
Lesson Agenda 3-27
Date-Manipulation Functions 3-28
Using Date Functions 3-29
Using ROUND and TRUNC Functions with Dates 3-30
Quiz 3-31
Summary 3-32
Practice 3: Overview 3-33
4
Using Conversion Functions and Conditional Expressions
Objectives 4-2
Lesson Agenda 4-3
Conversion Functions 4-4
Implicit Data Type Conversion 4-5
Explicit Data Type Conversion 4-7
Lesson Agenda 4-10
Using the TO_CHAR Function with Dates 4-11
Elements of the Date Format Model 4-12
Using the TO_CHAR Function with Dates 4-16
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Using the TO_CHAR Function with Numbers 4-17
Using the TO_NUMBER and TO_DATE Functions 4-20
Using the TO_CHAR and TO_DATE Function with RR Date Format 4-22
Lesson Agenda 4-23
Nesting Functions 4-24
Lesson Agenda 4-26
General Functions 4-27
NVL Function 4-28
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Using the NVL Function 4-29
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Using the NVL2 Function 4-30
Using the NULLIF Function 4-31
Using the COALESCE Function 4-32
Lesson Agenda 4-35
Conditional Expressions 4-36
CASE Expression 4-37
Using the CASE Expression 4-38
DECODE Function 4-39
Using the DECODE Function 4-40
Quiz 4-42
Summary 4-43
Practice 4: Overview 4-44
5
Reporting Aggregated Data Using the Group Functions
Objectives 5-2
Lesson Agenda 5-3
What Are Group Functions? 5-4
Types of Group Functions 5-5
Group Functions: Syntax 5-6
Using the AVG and SUM Functions 5-7
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Using the MIN and MAX Functions 5-8
Using the COUNT Function 5-9
Using the DISTINCT Keyword 5-10
Group Functions and Null Values 5-11
Lesson Agenda 5-12
Creating Groups of Data 5-13
Creating Groups of Data: GROUP BY Clause Syntax 5-14
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Using the GROUP BY Clause 5-15
Grouping by More than One Column 5-17
Using the GROUP BY Clause on Multiple Columns 5-18
Illegal Queries Using Group Functions 5-19
Restricting Group Results 5-21
Restricting Group Results with the HAVING Clause 5-22
Using the HAVING Clause 5-23
Lesson Agenda 5-25
Nesting Group Functions 5-26
Quiz 5-27
Summary 5-28
Practice 5: Overview 5-29
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6
Displaying Data from Multiple Tables
Objectives 6-2
Lesson Agenda 6-3
Obtaining Data from Multiple Tables 6-4
Types of Joins 6-5
Joining Tables Using SQL:1999 Syntax 6-6
Qualifying Ambiguous Column Names 6-7
Lesson Agenda 6-8
Creating Natural Joins 6-9
Retrieving Records with Natural Joins 6-10
Creating Joins with the USING Clause 6-11
Joining Column Names 6-12
Retrieving Records with the USING Clause 6-13
Using Table Aliases with the USING Clause 6-14
Creating Joins with the ON Clause 6-15
Retrieving Records with the ON Clause 6-16
Creating Three-Way Joins with the ON Clause 6-17
Applying Additional Conditions to a Join 6-18
Lesson Agenda 6-19
Joining a Table to Itself 6-20
Self-Joins Using the ON Clause 6-21
Lesson Agenda 6-22
Nonequijoins 6-23
Retrieving Records with Nonequijoins 6-24
Lesson Agenda 6-25
Returning Records with No Direct Match Using OUTER Joins 6-26
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INNER Versus OUTER Joins 6-27
LEFT OUTER JOIN 6-28
RIGHT OUTER JOIN 6-29
FULL OUTER JOIN 6-30
Lesson Agenda 6-31
Cartesian Products 6-32
Generating a Cartesian Product 6-33
Creating Cross Joins 6-34
Quiz 6-35
Summary 6-36
Practice 6: Overview 6-37
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7
Using Subqueries to Solve Queries
Objectives 7-2
Lesson Agenda 7-3
Using a Subquery to Solve a Problem 7-4
Subquery Syntax 7-5
Using a Subquery 7-6
Guidelines for Using Subqueries 7-7
Types of Subqueries 7-8
Lesson Agenda 7-9
Single-Row Subqueries 7-10
Executing Single-Row Subqueries 7-11
Using Group Functions in a Subquery 7-12
The HAVING Clause with Subqueries 7-13
What Is Wrong with This Statement? 7-14
No Rows Returned by the Inner Query 7-15
Lesson Agenda 7-16
Multiple-Row Subqueries 7-17
Using the ANY Operator in Multiple-Row Subqueries 7-18
Using the ALL Operator in Multiple-Row Subqueries 7-19
Lesson Agenda 7-20
Null Values in a Subquery 7-21
Quiz 7-23
Summary 7-24
Practice 7: Overview 7-25
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Using the Set Operators
Objectives 8-2
Lesson Agenda 8-3
Set Operators 8-4
Set Operator Guidelines 8-5
The Oracle Server and Set Operators 8-6
Lesson Agenda 8-7
Tables Used in This Lesson 8-8
Lesson Agenda 8-12
UNION Operator 8-13
Using the UNION Operator 8-14
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UNION ALL Operator 8-16
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Using the UNION ALL Operator 8-17
Lesson Agenda 8-18
INTERSECT Operator 8-19
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Using the INTERSECT Operator 8-20
Lesson Agenda 8-21
MINUS Operator 8-22
Using the MINUS Operator 8-23
Lesson Agenda 8-24
Matching the SELECT Statements 8-25
Matching the SELECT Statement: Example 8-26
Lesson Agenda 8-27
Using the ORDER BY Clause in Set Operations 8-28
Quiz 8-29
Summary 8-30
Practice 8: Overview 8-31
9
Manipulating Data
Objectives 9-2
Lesson Agenda 9-3
Data Manipulation Language 9-4
Adding a New Row to a Table 9-5
INSERT Statement Syntax 9-6
Inserting New Rows 9-7
Inserting Rows with Null Values 9-8
Inserting Special Values 9-9
Inserting Specific Date and Time Values 9-10
Creating a Script 9-11
Copying Rows from Another Table 9-12
Lesson Agenda 9-13
Changing Data in a Table 9-14
UPDATE Statement Syntax 9-15
Updating Rows in a Table 9-16
Updating Two Columns with a Subquery 9-17
Updating Rows Based on Another Table 9-18
Lesson Agenda 9-19
Removing a Row from a Table 9-20
DELETE Statement 9-21
Deleting Rows from a Table 9-22
Deleting Rows Based on Another Table 9-23
TRUNCATE Statement 9-24
Lesson Agenda 9-25
Database Transactions 9-26
Database Transactions: Start and End 9-27
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Advantages of COMMIT and ROLLBACK Statements 9-28
Explicit Transaction Control Statements 9-29
Rolling Back Changes to a Marker 9-30
Implicit Transaction Processing 9-31
State of the Data Before COMMIT or ROLLBACK 9-33
State of the Data After COMMIT 9-34
Committing Data 9-35
State of the Data After ROLLBACK 9-36
State of the Data After ROLLBACK: Example 9-37
Statement-Level Rollback 9-38
Lesson Agenda 9-39
Read Consistency 9-40
Implementing Read Consistency 9-41
Lesson Agenda 9-42
FOR UPDATE Clause in a SELECT Statement 9-43
FOR UPDATE Clause: Examples 9-44
Quiz 9-46
Summary 9-47
Practice 9: Overview 9-48
10 Using DDL Statements to Create and Manage Tables
Objectives 10-2
Lesson Agenda 10-3
Database Objects 10-4
Naming Rules 10-5
Lesson Agenda 10-6
CREATE TABLE Statement 10-7
Referencing Another User’s Tables 10-8
DEFAULT Option 10-9
Creating Tables 10-10
Lesson Agenda 10-11
Data Types 10-12
Datetime Data Types 10-14
Lesson Agenda 10-15
Including Constraints 10-16
Constraint Guidelines 10-17
Defining Constraints 10-18
NOT NULL Constraint 10-20
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UNIQUE Constraint 10-21
PRIMARY KEY Constraint 10-23
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FOREIGN KEY Constraint 10-24
FOREIGN KEY Constraint: Keywords 10-26
CHECK Constraint 10-27
CREATE TABLE: Example 10-28
Violating Constraints 10-29
Lesson Agenda 10-31
Creating a Table Using a Subquery 10-32
Lesson Agenda 10-34
ALTER TABLE Statement 10-35
Read-Only Tables 10-36
Lesson Agenda 10-37
Dropping a Table 10-38
Quiz 10-39
Summary 10-40
Practice 10: Overview 10-41
11 Creating Other Schema Objects
Objectives 11-2
Lesson Agenda 11-3
Database Objects 11-4
What Is a View? 11-5
Advantages of Views 11-6
Simple Views and Complex Views 11-7
Creating a View 11-8
Retrieving Data from a View 11-11
Modifying a View 11-12
Creating a Complex View 11-13
Rules for Performing DML Operations on a View 11-14
Using the WITH CHECK OPTION Clause 11-17
Denying DML Operations 11-18
Removing a View 11-20
Practice 11: Overview of Part 1 11-21
Lesson Agenda 11-22
Sequences 11-23
CREATE SEQUENCE Statement: Syntax 11-25
Creating a Sequence 11-26
NEXTVAL and CURRVAL Pseudocolumns 11-27
Using a Sequence 11-29
Caching Sequence Values 11-30
Modifying a Sequence 11-31
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Guidelines for Modifying a Sequence 11-32
Lesson Agenda 11-33
Indexes 11-34
How Are Indexes Created? 11-36
Creating an Index 11-37
Index Creation Guidelines 11-38
Removing an Index 11-39
Lesson Agenda 11-40
Synonyms 11-41
Creating a Synonym for an Object 11-42
Creating and Removing Synonyms 11-43
Quiz 11-44
Summary 11-45
Practice 11: Overview of Part 2 11-46
Appendix A: Practice Solutions
Appendix B: Table Descriptions
Appendix C: Oracle Join Syntax
Objectives C-2
Obtaining Data from Multiple Tables C-3
Cartesian Products C-4
Generating a Cartesian Product C-5
Types of Oracle-Proprietary Joins C-6
Joining Tables Using Oracle Syntax C-7
Qualifying Ambiguous Column Names C-8
Equijoins C-9
Retrieving Records with Equijoins C-10
Retrieving Records with Equijoins: Example C-11
Additional Search Conditions Using the AND Operator C-12
Joining More than Two Tables C-13
Nonequijoins C-14
Retrieving Records with Nonequijoins C-15
Returning Records with No Direct Match with Outer Joins C-16
Outer Joins: Syntax C-17
Using Outer Joins C-18
Outer Join: Another Example C-19
Joining a Table to Itself C-20
Self-Join: Example C-21
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Summary C-22
Practice C: Overview C-23
Appendix D: Using SQL*Plus
Objectives D-2
SQL and SQL*Plus Interaction D-3
SQL Statements Versus SQL*Plus Commands D-4
Overview of SQL*Plus D-5
Logging In to SQL*Plus D-6
Displaying Table Structure D-8
SQL*Plus Editing Commands D-10
Using LIST, n, and APPEND D-12
Using the CHANGE Command D-13
SQL*Plus File Commands D-14
Using the SAVE, START, and EDIT Commands D-15
SERVEROUTPUT Command D-17
Using the SQL*Plus SPOOL Command D-18
Using the AUTOTRACE Command D-19
Summary D-20
Appendix E: Using SQL Developer
Objectives E-2
What Is Oracle SQL Developer? E-3
Specifications of SQL Developer E-4
Installing SQL Developer E-5
SQL Developer 1.2 Interface E-6
Creating a Database Connection E-7
Browsing Database Objects E-10
Creating a Schema Object E-11
Creating a New Table: Example E-12
Using the SQL Worksheet E-13
Executing SQL Statements E-16
Saving SQL Scripts E-17
Executing Saved Script Files: Method 1 E-18
Executing Saved Script Files: Method 2 E-19
Executing SQL Statements E-20
Formatting the SQL Code E-21
Using Snippets E-22
Using Snippets: Example E-23
Using SQL*Plus E-24
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Debugging Procedures and Functions E-25
Database Reporting E-26
Creating a User-Defined Report E-27
Search Engines and External Tools E-28
Setting Preferences E-29
Specifications of SQL Developer 1.5.3 E-30
Installing SQL Developer 1.5.3 E-31
SQL Developer 1.5.3 Interface E-32
Summary E-34
Index
Additional Practices
Additional Practices: Solutions
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Preface
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Profile
Before You Begin This Course
Before you begin this course, you should be able to use a graphical user interface (GUI).
The prerequisite is a familiarity with data processing concepts and techniques.
How This Course Is Organized
Oracle Database 11g: SQL Fundamentals I is an instructor-led course featuring lectures
and hands-on exercises. Online demonstrations and written practice sessions reinforce the
concepts and skills that are introduced.
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Preface - 3
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Related Publications
Oracle Publications
Title
Part Number
Oracle® Database Reference 11g Release 1 (11.1)
B28320-01
Oracle® Database SQL Language Reference 11g
B28286-01
Release 1 (11.1)
Oracle® Database Concepts 11g Release 1 (11.1)
B28318-01
Oracle® Database SQL Developer User's Guide
E10406-01
Release 1.2
Additional Publications
•
System release bulletins
•
Installation and user’s guides
•
read.me files
•
International Oracle User’s Group (IOUG) articles
•
Oracle Magazine
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Preface - 4
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Typographic Conventions
What follows are two lists of typographical conventions that are used specifically within text or
within code.
Typographic Conventions Within Text
Convention
Object or Term
Example
Uppercase
Commands,
functions,
column names,
table names,
PL/SQL objects,
schemas
Use the SELECT command to view
information stored in the LAST_NAME
column of the EMPLOYEES table.
Lowercase,
italic
Filenames,
syntax variables,
usernames,
passwords
where: role
Initial cap
Trigger and
button names
Assign a When-Validate-Item trigger to
the ORD block.
is the name of the role
to be created.
Choose Cancel.
Italic
Quotation marks
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Books, names of
courses and
manuals, and
emphasized
words or phrases
For more information on the subject see
Oracle SQL Reference
Manual
Lesson module
titles referenced
within a course
This subject is covered in Lesson 3,
“Working with Objects.”
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Do not save changes to the database.
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Preface - 5
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Typographic Conventions (continued)
Typographic Conventions Within Code
Convention
Object or Term
Example
Uppercase
Commands,
functions
SELECT employee_id
FROM employees;
Lowercase,
italic
Syntax variables
CREATE ROLE role;
Initial cap
Forms triggers
Form module: ORD
Trigger level: S_ITEM.QUANTITY
item
Trigger name: When-Validate-Item
. . .
Lowercase
Column names,
table names,
filenames,
PL/SQL objects
. . .
OG_ACTIVATE_LAYER
(OG_GET_LAYER ('prod_pie_layer'))
. . .
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SELECT last_name
FROM
employees;
Bold
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Text that must
be entered by a
user
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CREATE USER scott
IDENTIFIED BY tiger;
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Preface - 6
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Introduction
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Lesson Objectives
After completing this lesson, you should be able to do the
following:
• Understand the goals of the course
• List the features of Oracle Database 11g
• Discuss the theoretical and physical aspects of a relational
database
• Describe Oracle server’s implementation of RDBMS and
object relational database management system
(ORDBMS)
• Identify the development environments that can be used
for this course
• Describe the database and schema used in this course
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Objectives
In this lesson, you gain an understanding of the relational database management system (RDBMS)
and the object relational database management system (ORDBMS). You are also introduced to
Oracle SQL Developer and SQL*Plus as development environments used for executing SQL
statements, and for formatting and reporting purposes.
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Oracle Database 11g: SQL Fundamentals I I - 2
Lesson Agenda
•
•
•
Course objectives, agenda, and appendixes used in the
course
Overview of Oracle Database 11g and related products
Overview of relational database management concepts
and terminologies
Introduction to SQL and its development environments
The HR schema and the tables used in this course
Oracle Database 11g documentation and additional
resources
•
•
•
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Oracle Database 11g: SQL Fundamentals I I - 3
Course Objectives
After completing this course, you should be able to:
• Identify the major components of Oracle Database 11g
• Retrieve row and column data from tables with the SELECT
statement
• Create reports of sorted and restricted data
• Employ SQL functions to generate and retrieve customized
data
• Run complex queries to retrieve data from multiple tables
• Run data manipulation language (DML) statements to
update data in Oracle Database 11g
• Run data definition language (DDL) statements to create
and manage schema objects
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Course Objectives
This course offers you an introduction to Oracle Database 11g database technology. In this class, you
learn the basic concepts of relational databases and the powerful SQL programming language. This
course provides the essential SQL skills that enable you to write queries against single and multiple
tables, manipulate data in tables, create database objects, and query metadata.
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Oracle Database 11g: SQL Fundamentals I I - 4
Course Agenda
•
Day 1:
– Introduction
– Retrieving Data Using the SQL SELECT Statement
– Restricting and Sorting Data
– Using Single-Row Functions to Customize Output
– Using Conversion Functions and Conditional Expressions
•
Day 2:
–
–
–
–
Reporting Aggregated Data Using the Group Functions
Displaying Data from Multiple Tables
Using Subqueries to Solve Queries
Using the Set Operators
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Oracle Database 11g: SQL Fundamentals I I - 5
Course Agenda
•
Day 3:
– Manipulating Data
– Using DDL Statements to Create and Manage Tables
– Creating Other Schema Objects
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Oracle Database 11g: SQL Fundamentals I I - 6
Appendixes Used in the Course
•
•
•
•
•
•
•
Appendix A: Practice Solutions
Appendix B: Table Descriptions
Appendix C: Oracle Join Syntax
Appendix D: Using SQL*Plus
Appendix E: Using SQL Developer
Additional Practices
Additional Practices Solutions
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Oracle Database 11g: SQL Fundamentals I I - 7
Lesson Agenda
•
•
•
Course objectives, course agenda, and appendixes used
in this course
Overview of Oracle Database 11g and related products
Overview of relational database management concepts
and terminologies
Introduction to SQL and its development environments
The HR schema and the tables used in this course
Oracle Database 11g documentation and additional
resources
•
•
•
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Oracle Database 11g: SQL Fundamentals I I - 8
Oracle Database 11g: Focus Areas
Infrastructure
Grids
Information
Management
Application
Development
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Oracle Database 11g: Focus Areas
Oracle Database 11g offers extensive features across the following focus areas:
• Infrastructure Grids: The Infrastructure Grid technology of Oracle enables pooling of low-cost
servers and storage to form systems that deliver the highest quality of service in terms of
manageability, high availability, and performance. Oracle Database 11g consolidates and
extends the benefits of grid computing. Apart from taking full advantage of grid computing,
Oracle Database 11g has unique change assurance features to manage changes in a controlled
and cost effective manner.
• Information Management: Oracle Database 11g extends the existing information management
capabilities in content management, information integration, and information life cycle
management areas. Oracle provides content management of advanced data types such as
Extensible Markup Language (XML), text, spatial, multimedia, medical imaging, and semantic
technologies.
• Application Development: Oracle Database 11g has capabilities to use and manage all the
major application development environments such as PL/SQL, Java/JDBC, .NET and Windows,
PHP, SQL Developer, and Application Express.
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Oracle Database 11g: SQL Fundamentals I I - 9
Oracle Database 11g
Manageability
High availability
Performance
Security
Information integration
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Oracle Database 11g
Organizations need to support multiple terabytes of information for users who demand fast and
secure access to business applications round-the-clock. The database systems must be reliable and
must be able to recover quickly in the event of any kind of failure. Oracle Database 11g is designed
along the following feature areas to help organizations manage infrastructure grids easily and deliver
high-quality service:
• Manageability: By using some of the change assurance, management automation, and fault
diagnostics features, the database administrators (DBAs) can increase their productivity, reduce
costs, minimize errors, and maximize quality of service. Some of the useful features that
promote better management are Database Replay facility, the SQL Performance Analyzer, and
the Automatic SQL Tuning facility.
• High availability: By using the high availability features, you can reduce the risk of down time
and data loss. These features improves online operations and enable faster database upgrades.
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Oracle Database 11g: SQL Fundamentals I I - 10
Oracle Database 11g
Manageability
High availability
Performance
Security
Information integration
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Oracle Database 11g (continued)
• Performance: By using capabilities such as SecureFiles, compression for online transaction
processing (OLTP), Real Application Clusters (RAC) optimizations, Result Caches and so on,
you can greatly improve the performance of your database. Oracle Database 11g enables
organizations to manage large, scalable transactional and data warehousing systems that deliver
fast data access using low-cost modular storage.
• Security: Oracle Database 11g helps organizations protect their information with unique secure
configurations, data encryption and masking, and sophisticated auditing capabilities. It delivers a
secure and scalable platform for reliable and fast access to all types of information by using the
industry-standard interfaces.
• Information integration: Oracle Database 11g has many features to better integrate data
throughout the enterprise. It also supports advanced information life cycle management
capabilities. This helps you manage the changing data in your database.
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Oracle Database 11g: SQL Fundamentals I I - 11
Oracle Fusion Middleware
Portfolio of leading, standards-based, and customer-proven
software products that spans a range of tools and services from
J2EE and developer tools, through integration services,
business intelligence, collaboration, and content management
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Oracle Fusion Middleware
Oracle Fusion Middleware is a comprehensive and well-integrated family of products that offers
complete support for development, deployment, and management of Service-Oriented Architecture
(SOA). SOA facilitates the development of modular business services that can be easily integrated
and reused, thereby reducing development and maintenance costs, and providing higher quality of
services. Oracle Fusion Middleware’s pluggable architecture enables you to leverage your
investments in any existing application, system, or technology. Its unbreakable core technology
minimizes the disruption caused by planned or unplanned outages.
Some of the products from the Oracle Fusion Middleware family include:
• Enterprise Application Server: Application Server
• Integration and Process Management: BPEL Process Manager, Oracle Business Process
Analysis Suite
• Development Tools: Oracle Application Development Framework, JDeveloper, SOA Suite
• Business Intelligence: Oracle Business Activity Monitoring, Oracle Data Integrator
• Systems Management: Enterprise Manager
• Identity Management: Oracle Identity Management
• Content Management: Oracle Content Database Suite
• User Interaction: Portal, WebCenter
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Oracle Database 11g: SQL Fundamentals I I - 12
Oracle Enterprise Manager Grid Control 10g
•
•
•
Efficient Oracle Fusion Middleware management
Simplifying application and infrastructure life cycle
management
Improved database administration and application
management capabilities
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Oracle Enterprise Manager Grid Control 10g
Spanning applications, middleware, and database management, Oracle Enterprise Manager Grid
Control 10g delivers integrated enterprise management for Oracle and non-Oracle systems.
Oracle Enterprise Manager Grid Control 10g features advanced Oracle Fusion Middleware
management capabilities for the services that business applications rely upon, including SOA,
Business Activity Monitoring, and Identity Management.
• Wide-ranging management functionality for your applications including service-level
management, application performance management, configuration management, and change
automation
• Built-in grid automation capabilities means that information technology responds proactively
to fluctuating demand and implements new services more quickly so that businesses can thrive.
• In-depth diagnostics and readily available remediation across a range of applications
including custom-built applications, Oracle E-Business Suite, PeopleSoft, Siebel, Oracle Fusion
Middleware, Oracle Database, and underlying infrastructure
• Extensive life cycle management capabilities extends grid computing by providing solutions
for the entire application and infrastructure life cycle, including test, stage, and production
through operations. It has simplified patch management with synchronized patching, additional
operating system support, and conflict detection features.
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Oracle Database 11g: SQL Fundamentals I I - 13
Oracle BI Publisher
•
•
Provides a central architecture for authoring, managing,
and delivering information in secure and multiple formats
Reduces complexity and time to develop, test, and deploy
all kinds of reports
– Financial Reports, Invoices, Sales or Purchase orders, XML,
and EDI/EFT(eText documents)
•
Enables flexible customizations
– For example, a Microsoft Word document report can be
generated in multiple formats such as PDF, HTML, Excel,
RTF, and so on.
PDF
Microsoft Word
BI PUBLISHER
HTML
Excel
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Oracle BI Publisher
Oracle Database 11g also includes Oracle BI Publisher—the enterprise reporting solution from
Oracle. Oracle BI Publisher (formerly known as XML Publisher) offers the most efficient and
scalable reporting solution available for complex, distributed environments.
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Oracle BI Publisher reduces the high costs associated with the development, customization, and
maintenance of business documents, while increasing the efficiency of reports management. By
using a set of familiar desktop tools, users can create and maintain their own report formats based on
data queries created by the IT staff or developers.
Oracle BI Publisher report formats can be designed using Microsoft Word or Adobe Acrobat—tools
that most users are already familiar with. Oracle BI Publisher also enables you to bring in data from
multiple data sources into a single output document. You can deliver reports via printer, email, or
fax. You can publish your report to a portal. You can even allow users to collaboratively edit and
manage reports on the Web-based Distributed Authoring and Versioning (WebDav) Web servers.
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Oracle Database 11g: SQL Fundamentals I I - 14
Lesson Agenda
•
•
•
Course objectives, course agenda, and appendixes used
in this course
Overview of Oracle Database 11g and related products
Overview of relational database management concepts
and terminologies
Introduction to SQL and its development environments
The HR schema and the tables used in this course
Oracle Database 11g documentation and additional
resources
•
•
•
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Oracle Database 11g: SQL Fundamentals I I - 15
Relational and Object Relational
Database Management Systems
•
•
•
•
•
Relational model and object relational model
User-defined data types and objects
Fully compatible with relational database
Supports multimedia and large objects
High-quality database server features
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Relational and Object Relational Database Management Systems
The Oracle server supports both the relational and the object relational database models.
The Oracle server extends the data-modeling capabilities to support an object relational database
model that provides object-oriented programming, complex data types, complex business objects,
and full compatibility with the relational world.
It includes several features for improved performance and functionality of the OLTP applications,
such as better sharing of run-time data structures, larger buffer caches, and deferrable constraints.
Data warehouse applications benefit from enhancements such as parallel execution of insert, update,
and delete operations; partitioning; and parallel-aware query optimization. The Oracle model
supports client/server and Web-based applications that are distributed and multitiered.
For more information about the relational and object relational model, see the Oracle Database
Concepts 11g Release 1 (11.1) manual.
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Oracle Database 11g: SQL Fundamentals I I - 16
Data Storage on Different Media
Electronic
spreadsheet
Filing cabinet
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Database
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Data Storage on Different Media
Every organization has some information needs. A library keeps a list of members, books, due dates,
and fines. A company needs to save information about its employees, departments, and salaries.
These pieces of information are called data.
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Organizations can store data in various media and in different formats, such as a hard copy document
in a filing cabinet, or data stored in electronic spreadsheets, or in databases.
A database is an organized collection of information.
To manage databases, you need a database management system (DBMS). A DBMS is a program that
stores, retrieves, and modifies data in databases on request. There are four main types of databases:
hierarchical, network, relational, and (most recently) object relational.
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Oracle Database 11g: SQL Fundamentals I I - 17
Relational Database Concept
•
•
Dr. E. F. Codd proposed the relational model for database
systems in 1970.
It is the basis for the relational database management
system (RDBMS).
The relational model consists of the following:
•
– Collection of objects or relations
– Set of operators to act on the relations
– Data integrity for accuracy and consistency
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Relational Database Concept
The principles of the relational model were first outlined by Dr. E. F. Codd in a June 1970 paper
titled “A Relational Model of Data for Large Shared Data Banks.” In this paper, Dr. Codd proposed
the relational model for database systems.
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The common models used at that time were hierarchical and network, or even simple flat-file data
structures. Relational database management systems (RDBMS) soon became very popular, especially
for their ease of use and flexibility in structure. In addition, a number of innovative vendors, such as
Oracle, supplemented the RDBMS with a suite of powerful, application development and userinterface products, thereby providing a total solution.
Components of the Relational Model
• Collections of objects or relations that store the data
• A set of operators that can act on the relations to produce other relations
• Data integrity for accuracy and consistency
For more information, see An Introduction to Database Systems, Eighth Edition (Addison-Wesley:
2004), written by Chris Date.
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Oracle Database 11g: SQL Fundamentals I I - 18
Definition of a Relational Database
A relational database is a collection of relations or
two-dimensional tables.
Oracle
server
Table name: EMPLOYEES
…
Table name: DEPARTMENTS
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…
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Definition of a Relational Database
A relational database uses relations or two-dimensional tables to store information.
For example, you might want to store information about all the employees in your company. In a
relational database, you create several tables to store different pieces of information about your
employees, such as an employee table, a department table, and a salary table.
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Oracle Database 11g: SQL Fundamentals I I - 19
Data Models
Model of
system
in client’s
mind
Entity model of
client’s model
Table model
of entity model
Oracle
server
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Tables on disk
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Data Models
Models are the cornerstone of design. Engineers build a model of a car to work out any details before
putting it into production. In the same manner, system designers develop models to explore ideas and
improve the understanding of database design.
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Purpose of Models
Models help communicate the concepts that are in people’s minds. They can be used to do the
following:
• Communicate
• Categorize
• Describe
• Specify
• Investigate
• Evolve
• Analyze
• Imitate
The objective is to produce a model that fits a multitude of these uses, can be understood by an end
user, and contains sufficient detail for a developer to build a database system.
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Oracle Database 11g: SQL Fundamentals I I - 20
Entity Relationship Model
•
Create an entity relationship diagram from business
specifications or narratives:
EMPLOYEE
#*
number
*
name
o
job title
•
DEPARTMENT
#*
number
*
name
composed of o
location
assigned to
Scenario:
– “. . . Assign one or more employees to a
department . . .”
– “. . . Some departments do not yet have assigned employees
. . .”
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Entity Relationship Model
In an effective system, data is divided into discrete categories or entities. An entity relationship (ER)
model is an illustration of the various entities in a business and the relationships among them. An ER
model is derived from business specifications or narratives and built during the analysis phase of the
system development life cycle. ER models separate the information required by a business from the
activities performed within the business. Although businesses can change their activities, the type of
information tends to remain constant. Therefore, the data structures also tend to be constant.
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Oracle Database 11g: SQL Fundamentals I I - 21
Entity Relationship Model (continued)
Benefits of ER Modeling:
• Documents information for the organization in a clear, precise format
• Provides a clear picture of the scope of the information requirement
• Provides an easily understood pictorial map for database design
• Offers an effective framework for integrating multiple applications
Key Components
• Entity: An aspect of significance about which information must be known. Examples are
departments, employees, and orders.
• Attribute: Something that describes or qualifies an entity. For example, for the employee entity,
the attributes would be the employee number, name, job title, hire date, department number, and
so on. Each of the attributes is either required or optional. This state is called optionality.
• Relationship: A named association between entities showing optionality and degree. Examples
are employees and departments, and orders and items
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Oracle Database 11g: SQL Fundamentals I I - 22
Entity Relationship
Modeling Conventions
Attribute:
Entity:
• Singular, unique name • Singular name
• Lowercase
• Uppercase
• Mandatory marked with “*”
• Soft box
• Optional marked with “o”
• Synonym in parentheses
EMPLOYEE
#*
number
*
name
o
job title
DEPARTMENT
#*
number
*
name
composed of o
location
assigned to
Unique Identifier (UID)
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Primary marked with “#”
Secondary marked with “(#)”
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ER Modeling Conventions
Entities
To represent an entity in a model, use the following conventions:
• Singular, unique entity name
• Entity name in uppercase
• Soft box
• Optional synonym names in uppercase within parentheses: ( )
Attributes
To represent an attribute in a model, use the following conventions:
• Singular name in lowercase
• Asterisk (*) tag for mandatory attributes (that is, values that must be known)
• Letter “o” tag for optional attributes (that is, values that may be known)
Relationships
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Symbol
O
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Description
Dashed line
Solid line
Crow’s foot
Optional element indicating “maybe”
Mandatory element indicating “must be”
Degree element indicating “one or more”
Single line
Degree element indicating “one and only one”
Oracle Database 11g: SQL Fundamentals I I - 23
ER Modeling Conventions (continued)
Relationships
Each direction of the relationship contains:
• A label: for example, taught by or assigned to
• An optionality: either must be or maybe
• A degree: either one and only one or one or more
Note: The term cardinality is a synonym for the term degree.
Each source entity {may be | must be} in relation {one and only one | one or more} with the
destination entity.
Note: The convention is to read clockwise.
Unique Identifiers
A unique identifier (UID) is any combination of attributes or relationships, or both, that serves to
distinguish occurrences of an entity. Each entity occurrence must be uniquely identifiable.
• Tag each attribute that is part of the UID with a hash sign “#”.
• Tag secondary UIDs with a hash sign in parentheses (#).
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Oracle Database 11g: SQL Fundamentals I I - 24
Relating Multiple Tables
•
Each row of data in a table is uniquely identified by a
primary key.
You can logically relate data from multiple tables using
foreign keys.
•
Table name: DEPARTMENTS
Table name: EMPLOYEES
…
Primary key
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Foreign key Primary key
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Relating Multiple Tables
Each table contains data that describes exactly one entity. For example, the EMPLOYEES table
contains information about employees. Categories of data are listed across the top of each table, and
individual cases are listed below. By using a table format, you can readily visualize, understand, and
use information.
Because data about different entities is stored in different tables, you may need to combine two or
more tables to answer a particular question. For example, you may want to know the location of the
department where an employee works. In this scenario, you need information from the EMPLOYEES
table (which contains data about employees) and the DEPARTMENTS table (which contains
information about departments). With an RDBMS, you can relate the data in one table to the data in
another by using the foreign keys. A foreign key is a column (or a set of columns) that refers to a
primary key in the same table or another table.
You can use the ability to relate data in one table to data in another to organize information in
separate, manageable units. Employee data can be kept logically distinct from the department data by
storing it in a separate table.
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Oracle Database 11g: SQL Fundamentals I I - 25
Relating Multiple Tables (continued)
Guidelines for Primary Keys and Foreign Keys
• You cannot use duplicate values in a primary key.
• Primary keys generally cannot be changed.
• Foreign keys are based on data values and are purely logical (not physical) pointers.
• A foreign key value must match an existing primary key value or unique key value, otherwise it
must be null.
• A foreign key must reference either a primary key or a unique key column.
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Oracle Database 11g: SQL Fundamentals I I - 26
Relational Database Terminology
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Relational Database Terminology
A relational database can contain one or many tables. A table is the basic storage structure of an
RDBMS. A table holds all the data necessary about something in the real world, such as employees,
invoices, or customers.
The slide shows the contents of the EMPLOYEES table or relation. The numbers indicate the
following:
1. A single row (or tuple) representing all the data required for a particular employee. Each row in
a table should be identified by a primary key, which permits no duplicate rows. The order of
rows is insignificant; specify the row order when the data is retrieved.
2. A column or attribute containing the employee number. The employee number identifies a
unique employee in the EMPLOYEES table. In this example, the employee number column is
designated as the primary key. A primary key must contain a value and the value must be
unique.
3. A column that is not a key value. A column represents one kind of data in a table; in this
example, the data is the salaries of all the employees. Column order is insignificant when storing
data; specify the column order when the data is retrieved.
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Oracle Database 11g: SQL Fundamentals I I - 27
Relational Database Terminology (continued)
4. A column containing the department number, which is also a foreign key. A foreign key is a
column that defines how tables relate to each other. A foreign key refers to a primary key or a
unique key in the same table or in another table. In the example, DEPARTMENT_ID uniquely
identifies a department in the DEPARTMENTS table.
5. A field can be found at the intersection of a row and a column. There can be only one value in it.
6. A field may have no value in it. This is called a null value. In the EMPLOYEES table, only those
employees who have the role of sales representative have a value in the COMMISSION_PCT
(commission) field.
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Oracle Database 11g: SQL Fundamentals I I - 28
Lesson Agenda
•
•
•
Course objectives, course agenda, and appendixes used
in this course
Overview of Oracle Database 11g and related products
Overview of relational database management concepts
and terminologies
Introduction to SQL and its development environments
The HR schema and the tables used in this course
Oracle Database 11g documentation and additional
resources
•
•
•
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Oracle Database 11g: SQL Fundamentals I I - 29
Using SQL to Query Your Database
Structured query language (SQL) is:
• The ANSI standard language for operating relational
databases
• Efficient, easy to learn, and use
• Functionally complete (With SQL, you can define, retrieve,
and manipulate data in the tables.)
SELECT department_name
FROM
departments;
Oracle
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Using SQL to Query Your Database
In a relational database, you do not specify the access route to the tables, and you do not need to
know how the data is arranged physically.
To access the database, you execute a structured query language (SQL) statement, which is the
American National Standards Institute (ANSI) standard language for operating relational databases.
SQL is a set of statements with which all programs and users access data in an Oracle database.
Application programs and Oracle tools often allow users access to the database without using SQL
directly, but these applications, in turn, must use SQL when executing the user’s request.
SQL provides statements for a variety of tasks, including:
• Querying data
• Inserting, updating, and deleting rows in a table
• Creating, replacing, altering, and dropping objects
• Controlling access to the database and its objects
• Guaranteeing database consistency and integrity
SQL unifies all of the preceding tasks in one consistent language and enables you to work with data
at a logical level.
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Oracle Database 11g: SQL Fundamentals I I - 30
SQL Statements
SELECT
INSERT
UPDATE
DELETE
MERGE
Data manipulation language (DML)
CREATE
ALTER
DROP
RENAME
TRUNCATE
COMMENT
Data definition language (DDL)
GRANT
REVOKE
Data control language (DCL)
COMMIT
ROLLBACK
SAVEPOINT
Transaction control
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SQL Statements
SQL statements supported by Oracle comply with industry standards. Oracle Corporation ensures
future compliance with evolving standards by actively involving key personnel in SQL standards
committees. The industry-accepted committees are ANSI and International Standards Organization
(ISO). Both ANSI and ISO have accepted SQL as the standard language for relational databases.
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Statement
Description
SELECT
INSERT
UPDATE
DELETE
MERGE
CREATE
ALTER
DROP
RENAME
TRUNCATE
COMMENT
GRANT
REVOKE
Retrieves data from the database, enters new rows, changes existing rows, and
removes unwanted rows from tables in the database, respectively. Collectively
known as data manipulation language (DML)
COMMIT
ROLLBACK
SAVEPOINT
Manages the changes made by DML statements. Changes to the data can be
grouped together into logical transactions
Sets up, changes, and removes data structures from tables. Collectively known as
data definition language (DDL)
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Provides or removes access rights to both the Oracle database and the structures
within it
Oracle Database 11g: SQL Fundamentals I I - 31
Development Environments for SQL
There are two development environments for this course:
• Primary tool is Oracle SQL Developer
• SQL*Plus command line interface may also be used
SQL Developer
SQL *Plus
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Development Environments for SQL
SQL Developer
This course has been developed using Oracle SQL Developer as the tool for running the SQL
statements discussed in the examples in the slide and the practices.
• SQL Developer version 1.2 is shipped with Oracle Database 11g, and is the default tool for this
class.
• In addition, SQL Developer version 1.5.3 is also available on the classroom machine, and may
be installed for use. At the time of publication for this course, version 1.5.3 was the latest release
of SQL Developer.
SQL*Plus
The SQL*Plus environment may also be used to run all SQL commands covered in this course.
Note
• See Appendix E for information on using SQL Developer, including simple instructions on
installing version 1.5.3.
• See Appendix D for information on using SQL*Plus.
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Oracle Database 11g: SQL Fundamentals I I - 32
Lesson Agenda
•
•
•
Course objectives, course agenda, and appendixes used
in this course
Overview of Oracle Database 11g and related products
Overview of relational database management concepts
and terminologies
Introduction to SQL and its development environments
The HR schema and the tables used in this course
Oracle Database 11g documentation and additional
resources
•
•
•
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Oracle Database 11g: SQL Fundamentals I I - 33
The Human Resources (HR) Schema
DEPARTMENTS
department_id
department_name
manager_id
location_id
LOCATIONS
location_id
street_address
postal_code
city
state_province
country_id
JOB_HISTORY
employee_id
start_date
end_date
job_id
department_id
JOBS
job_id
job_title
min_salary
max_salary
EMPLOYEES
employee_id
first_name
last_name
email
phone_number
hire_date
job_id
salary
commission_pct
manager_id
department_id
COUNTRIES
country_id
country_name
region_id
REGIONS
region_id
region_name
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Copyright © 2009, Oracle. All rights reserved.
The Human Resources (HR)Schema Description
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The Human Resources (HR) schema is a part of the Oracle Sample Schemas that can be installed in
an Oracle database. The practice sessions in this course use data from the HR schema.
Table Descriptions
• REGIONS contains rows that represent a region such as America, Asia, and so on.
• COUNTRIES contains rows for countries, each of which is associated with a region.
• LOCATIONS contains the specific address of a specific office, warehouse, or production site of
a company in a particular country.
• DEPARTMENTS shows details about the departments in which the employees work. Each
department may have a relationship representing the department manager in the EMPLOYEES
table.
• EMPLOYEES contains details about each employee working for a department. Some employees
may not be assigned to any department.
• JOBS contains the job types that can be held by each employee.
• JOB_HISTORY contains the job history of the employees. If an employee changes departments
within a job or changes jobs within a department, then a new row is inserted into this table with
the earlier job information of the employee.
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Oracle Database 11g: SQL Fundamentals I I - 34
Tables Used in the Course
EMPLOYEES
DEPARTMENTS
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JOB_GRADES
Copyright © 2009, Oracle. All rights reserved.
Tables Used in the Course
The following main tables are used in this course:
• EMPLOYEES table: Gives details of all the employees
• DEPARTMENTS table: Gives details of all the departments
• JOB_GRADES table: Gives details of salaries for various grades
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Apart from these tables, you will also use the other tables listed in the previous slide such as the
LOCATIONS and the JOB_HISTORY table.
Note: The structure and data for all the tables are provided in Appendix B.
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Oracle Database 11g: SQL Fundamentals I I - 35
Lesson Agenda
•
•
•
Course objectives, course agenda, and appendixes used
in this course
Overview of Oracle Database 11g and related products
Overview of relational database management concepts
and terminologies
Introduction to SQL and its development environments
The HR schema and the tables used in this course
Oracle Database 11g documentation and additional
resources
•
•
•
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Oracle Database 11g: SQL Fundamentals I I - 36
Oracle Database 11g Documentation
•
•
•
Oracle Database New Features Guide 11g,
Release 1 (11.1)
Oracle Database Reference 11g, Release 1 (11.1)
Oracle Database SQL Language Reference 11g,
Release 1 (11.1)
Oracle Database Concepts 11g, Release 1 (11.1)
Oracle Database SQL Developer User's Guide,
Release 1.2
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Oracle Database 11g Documentation
Navigate to http://www.oracle.com/pls/db111/homepage to access the Oracle Database 11g
documentation library.
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Oracle Database 11g: SQL Fundamentals I I - 37
Additional Resources
For additional information about the Oracle Database 11g, refer
to the following:
• Oracle Database 11g: New Features eStudies
• Oracle by Example series (OBE): Oracle Database 11g
– http://www.oracle.com/technology/obe/11gr1_db/index.htm
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Oracle Database 11g: SQL Fundamentals I I - 38
Summary
In this lesson, you should have learned that:
• Oracle Database 11g extends:
– The benefits of infrastructure grids
– The existing information management capabilities
– The capabilities to use the major application development
environments such as PL/SQL, Java/JDBC, .NET, XML, and
so on
•
•
•
The database is based on ORDBMS
Relational databases are composed of relations, managed
by relational operations, and governed by data integrity
constraints
With the Oracle server, you can store and manage
information by using SQL
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Summary
Relational database management systems are composed of objects or relations. They are managed by
operations and governed by data integrity constraints.
Oracle Corporation produces products and services to meet your RDBMS needs. The main products
are the following:
• Oracle Database 11g with which you store and manage information by using SQL
• Oracle Fusion Middleware with which you develop, deploy, and manage modular business
services that can be integrated and reused
• Oracle Enterprise Manager Grid Control 10g, which you use to manage and automate
administrative tasks across sets of systems in a grid environment
SQL
The Oracle server supports ANSI-standard SQL and contains extensions. SQL is the language that is
used to communicate with the server to access, manipulate, and control data.
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Oracle Database 11g: SQL Fundamentals I I - 39
Practice I: Overview
This practice covers the following topics:
• Running the Oracle SQL Developer demo
• Starting Oracle SQL Developer, creating a new database
connection, and browsing the HR tables
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Practice I: Overview
In this practice, you perform the following:
• Run through the Oracle SQL Developer demo.
• Use Oracle SQL Developer to examine data objects in the ORA account assigned to you. The
ORA accounts contain the HR schema tables.
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Note the following location for the lab files:
D:\labs\SQL1\labs
If you are asked to save any lab files, save them in this location.
In any practice, there maybe exercises that are prefaced with the phrases “If you have time” or “If
you want an extra challenge.” Work on these exercises only if you have completed all other exercises
within the allocated time and would like a further challenge to your skills.
Perform the practices slowly and precisely. You can experiment with saving and running command
files. If you have any questions at any time, ask your instructor.
Note: All written practices use Oracle SQL Developer as the development environment. Although it
is recommended that you use Oracle SQL Developer, you can also use SQL*Plus that is available in
this course.
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Oracle Database 11g: SQL Fundamentals I I - 40
Practice I
This is the first of many practices in this course. The solutions (if you require them) can be found in
Appendix A. Practices are intended to cover most of the topics that are presented in the
corresponding lesson.
Run Through the Oracle SQL Developer Demo: Creating a Database Connection
1. Access the demo “Creating a database connection” at:
http://st-curriculum.oracle.com/tutorial/SQLDeveloper/html/module2/mod02_cp_newdbconn.htm
Starting Oracle SQL Developer
2. Start Oracle SQL Developer using the sqldeveloper desktop icon.
Note: When you start SQL Developer for the first time, you need to provide the path to the
java.exe file. This is already done for you as a part of the classroom setup. In any case, if
you are prompted, enter the following path:
D:\app\Administrator\product\11.1.0\client_1\jdevstudio\jdk\bin
Creating a New Oracle SQL Developer Database Connection
3. To create a new database connection, in the Connections Navigator, right-click Connections.
Select New Connection from the menu. The New/Select Database Connection dialog box
appears.
4. Create a database connection using the following information:
a. Connection Name: myconnection.
b. Username: oraxx where xx is the number of your PC (Ask your instructor to assign you
one ora account out of the ora1-ora20 range of accounts.).
c. Password: oraxx
d. Hostname: Enter the host name of the machine where your database server is running.
e. Port: 1521
f. SID: ORCL
g. Ensure that you select the Save Password check box.
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Oracle Database 11g: SQL Fundamentals I I - 41
Practice I (continued)
Testing and Connecting Using the Oracle SQL Developer Database Connection
5. Test the new connection.
6. If the status is Success, connect to the database using this new connection.
Browsing the Tables in the Connections Navigator
7. In the Connections Navigator, view the objects available to you in the Tables node. Verify that
the following tables are present:
COUNTRIES
DEPARTMENTS
EMPLOYEES
JOB_GRADES
JOB_HISTORY
JOBS
LOCATIONS
REGIONS
8. Browse the structure of the EMPLOYEES table.
9. View the data of the DEPARTMENTS table.
Opening a SQL Worksheet
10.Open a new SQL Worksheet. Examine the shortcut icons available for the SQL Worksheet.
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Oracle Database 11g: SQL Fundamentals I I - 42
Retrieving Data Using
the SQL SELECT Statement
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Objectives
After completing this lesson, you should be able to do the
following:
• List the capabilities of SQL SELECT statements
• Execute a basic SELECT statement
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Objectives
To extract data from the database, you need to use the SQL SELECT statement. However, you may
need to restrict the columns that are displayed. This lesson describes all the SQL statements that are
needed to perform these actions. Further, you may want to create SELECT statements that can be
used more than once.
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Oracle Database 11g: SQL Fundamentals I 1 - 2
Lesson Agenda
•
•
•
•
Basic SELECT statement
Arithmetic expressions and NULL values in the SELECT
statement
Column aliases
Use of concatenation operator, literal character strings,
alternative quote operator, and the DISTINCT keyword
DESCRIBE command
•
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Oracle Database 11g: SQL Fundamentals I 1 - 3
Capabilities of SQL SELECT Statements
Projection
Selection
Table 1
Table 1
Join
Table 1
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Table 2
Copyright © 2009, Oracle. All rights reserved.
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Capabilities of SQL SELECT Statements
A SELECT statement retrieves information from the database. With a SELECT statement, you can
use the following capabilities:
• Projection: Select the columns in a table that are returned by a query. Select as few or as many
of the columns as required.
• Selection: Select the rows in a table that are returned by a query. Various criteria can be used to
restrict the rows that are retrieved.
• Joining: Bring together data that is stored in different tables by specifying the link between
them. SQL joins are covered in more detail in the lesson titled “Displaying Data from Multiple
Tables.”
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Oracle Database 11g: SQL Fundamentals I 1 - 4
Basic SELECT Statement
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM
table;
•
•
SELECT identifies the columns to be displayed.
FROM identifies the table containing those columns.
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Basic SELECT Statement
In its simplest form, a SELECT statement must include the following:
• A SELECT clause, which specifies the columns to be displayed
• A FROM clause, which identifies the table containing the columns that are listed in the SELECT
clause
In the syntax:
SELECT
is a list of one or more columns
*
selects all columns
DISTINCT
suppresses duplicates
column|expression
selects the named column or the expression
alias
gives the selected columns different headings
FROM table
specifies the table containing the columns
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Note: Throughout this course, the words keyword, clause, and statement are used as follows:
• A keyword refers to an individual SQL element.
For example, SELECT and FROM are keywords.
• A clause is a part of a SQL statement.
For example, SELECT employee_id, last_name, and so on is a clause.
• A statement is a combination of two or more clauses.
For example, SELECT * FROM employees is a SQL statement.
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Oracle Database 11g: SQL Fundamentals I 1 - 5
Selecting All Columns
SELECT *
FROM
departments;
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Selecting All Columns
You can display all columns of data in a table by following the SELECT keyword with an asterisk
(*). In the example in the slide, the department table contains four columns: DEPARTMENT_ID,
DEPARTMENT_NAME, MANAGER_ID, and LOCATION_ID. The table contains eight rows, one for
each department.
You can also display all columns in the table by listing all the columns after the SELECT keyword.
For example, the following SQL statement (like the example in the slide) displays all columns and all
rows of the DEPARTMENTS table:
SELECT
FROM
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department_id, department_name, manager_id, location_id
departments;
Note: In SQL Developer, you can enter your SQL statement in a SQL Worksheet and click the
“Execute Statement” icon or press [F9] to execute the statement. The output displayed in the Results
tabbed page appears as shown in the slide.
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Oracle Database 11g: SQL Fundamentals I 1 - 6
Selecting Specific Columns
SELECT department_id, location_id
FROM
departments;
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Selecting Specific Columns
You can use the SELECT statement to display specific columns of the table by specifying the column
names, separated by commas. The example in the slide displays all the department numbers and
location numbers from the DEPARTMENTS table.
In the SELECT clause, specify the columns that you want in the order in which you want them to
appear in the output. For example, to display location before department number (from left to right),
you use the following statement:
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SELECT location_id, department_id
FROM
departments;
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Oracle Database 11g: SQL Fundamentals I 1 - 7
Writing SQL Statements
•
•
•
•
•
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SQL statements are not case-sensitive.
SQL statements can be entered on one or more lines.
Keywords cannot be abbreviated or split across lines.
Clauses are usually placed on separate lines.
Indents are used to enhance readability.
In SQL Developer, SQL statements can optionally be
terminated by a semicolon (;). Semicolons are required
when you execute multiple SQL statements.
In SQL*Plus, you are required to end each SQL statement
with a semicolon (;).
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Writing SQL Statements
By using the following simple rules and guidelines, you can construct valid statements that are both
easy to read and edit:
• SQL statements are not case-sensitive (unless indicated).
• SQL statements can be entered on one or many lines.
• Keywords cannot be split across lines or abbreviated.
• Clauses are usually placed on separate lines for readability and ease of editing.
• Indents should be used to make code more readable.
• Keywords typically are entered in uppercase; all other words, such as table names and columns
names are entered in lowercase.
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Executing SQL Statements
In SQL Developer, click the Run Script icon or press [F5] to run the command or commands in the
SQL Worksheet. You can also click the Execute Statement icon or press [F9] to run a SQL statement
in the SQL Worksheet. The Execute Statement icon executes the statement at the mouse pointer in
the Enter SQL Statement box while the Run Script icon executes all the statements in the Enter SQL
Statement box. The Execute Statement icon displays the output of the query on the Results tabbed
page while the Run Script icon emulates the SQL*Plus display and shows the output on the Script
Output tabbed page.
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In SQL*Plus, terminate the SQL statement with a semicolon, and then press [Enter] to run the
command.
Oracle Database 11g: SQL Fundamentals I 1 - 8
Column Heading Defaults
•
SQL Developer:
– Default heading alignment: Left-aligned
– Default heading display: Uppercase
•
SQL*Plus:
– Character and Date column headings are left-aligned.
– Number column headings are right-aligned.
– Default heading display: Uppercase
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Column Heading Defaults
In SQL Developer, column headings are displayed in uppercase and are left-aligned.
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SELECT last_name, hire_date, salary
FROM
employees;
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You can override the column heading display with an alias. Column aliases are covered later in this
lesson.
Oracle Database 11g: SQL Fundamentals I 1 - 9
Lesson Agenda
•
•
•
•
Basic SELECT statement
Arithmetic expressions and NULL values in the SELECT
statement
Column Aliases
Use of concatenation operator, literal character strings,
alternative quote operator, and the DISTINCT keyword
DESCRIBE command
•
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Oracle Database 11g: SQL Fundamentals I 1 - 10
Arithmetic Expressions
Create expressions with number and date data by using
arithmetic operators.
Operator
Description
+
Add
-
Subtract
*
Multiply
/
Divide
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Arithmetic Expressions
You may need to modify the way in which data is displayed, or you may want to perform
calculations, or look at what-if scenarios. All these are possible using arithmetic expressions. An
arithmetic expression can contain column names, constant numeric values, and the arithmetic
operators.
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Arithmetic Operators
The slide lists the arithmetic operators that are available in SQL. You can use arithmetic operators in
any clause of a SQL statement (except the FROM clause).
Note: With the DATE and TIMESTAMP data types, you can use the addition and subtraction
operators only.
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Oracle Database 11g: SQL Fundamentals I 1 - 11
Using Arithmetic Operators
SELECT last_name, salary, salary + 300
FROM
employees;
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Using Arithmetic Operators
The example in the slide uses the addition operator to calculate a salary increase of $300 for all
employees. The slide also displays a SALARY+300 column in the output.
Note that the resultant calculated column, SALARY+300, is not a new column in the EMPLOYEES
table; it is for display only. By default, the name of a new column comes from the calculation that
generated it—in this case, salary+300.
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Note: The Oracle server ignores blank spaces before and after the arithmetic operator.
Operator Precedence
If an arithmetic expression contains more than one operator, multiplication and division are evaluated
first. If operators in an expression are of the same priority, then evaluation is done from left to right.
You can use parentheses to force the expression that is enclosed by the parentheses to be evaluated
first.
Rules of Precedence:
• Multiplication and division occur before addition and subtraction.
• Operators of the same priority are evaluated from left to right.
• Parentheses are used to override the default precedence or to clarify the statement.
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Oracle Database 11g: SQL Fundamentals I 1 - 12
Operator Precedence
SELECT last_name, salary, 12*salary+100
FROM
employees;
1
…
SELECT last_name, salary, 12*(salary+100)
FROM
employees;
2
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Operator Precedence (continued)
The first example in the slide displays the last name, salary, and annual compensation of employees.
It calculates the annual compensation by multiplying the monthly salary with 12, plus a one-time
bonus of $100. Note that multiplication is performed before addition.
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Note: Use parentheses to reinforce the standard order of precedence and to improve clarity. For
example, the expression in the slide can be written as (12*salary)+100 with no change in the
result.
Using Parentheses
You can override the rules of precedence by using parentheses to specify the desired order in which
the operators are to be executed.
The second example in the slide displays the last name, salary, and annual compensation of
employees. It calculates the annual compensation as follows: adding a monthly bonus of $100 to the
monthly salary, and then multiplying that subtotal with 12. Because of the parentheses, addition takes
priority over multiplication.
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Oracle Database 11g: SQL Fundamentals I 1 - 13
Defining a Null Value
•
Null is a value that is unavailable, unassigned, unknown,
or inapplicable.
Null is not the same as zero or a blank space.
•
SELECT last_name, job_id, salary, commission_pct
FROM
employees;
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Defining a Null Value
If a row lacks a data value for a particular column, that value is said to be null or to contain a null.
Null is a value that is unavailable, unassigned, unknown, or inapplicable. Null is not the same as zero
or a blank space. Zero is a number and blank space is a character.
Columns of any data type can contain nulls. However, some constraints (NOT NULL and PRIMARY
KEY) prevent nulls from being used in the column.
In the COMMISSION_PCT column in the EMPLOYEES table, notice that only a sales manager or
sales representative can earn a commission. Other employees are not entitled to earn commissions. A
null represents that fact.
Note: By default, SQL Developer uses the literal, (null), to identify null values. However, you can
set it to something more relevant to you. To do so, select Preferences from the Tools menu. In the
Preferences dialog box, expand the Database node. Click Advanced Parameters and on the right
pane, for the “Display Null value As,” enter the appropriate value.
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Oracle Database 11g: SQL Fundamentals I 1 - 14
Null Values in Arithmetic Expressions
Arithmetic expressions containing a null value evaluate to null.
SELECT last_name, 12*salary*commission_pct
FROM
employees;
…
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Null Values in Arithmetic Expressions
If any column value in an arithmetic expression is null, the result is null. For example, if you attempt
to perform division by zero, you get an error. However, if you divide a number by null, the result is a
null or unknown.
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In the example in the slide, employee King does not get any commission. Because the
COMMISSION_PCT column in the arithmetic expression is null, the result is null.
For more information, see the section on “Basic Elements of Oracle SQL” in Oracle Database SQL
Language Reference 11g, Release 1 (11.1).
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Oracle Database 11g: SQL Fundamentals I 1 - 15
Lesson Agenda
•
•
•
•
Basic SELECT statement
Arithmetic expressions and NULL values in the SELECT
statement
Column aliases
Use of concatenation operator, literal character strings,
alternative quote operator, and the DISTINCT keyword
DESCRIBE command
•
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Oracle Database 11g: SQL Fundamentals I 1 - 16
Defining a Column Alias
A column alias:
• Renames a column heading
• Is useful with calculations
• Immediately follows the column name (There can also be
the optional AS keyword between the column name and
alias.)
• Requires double quotation marks if it contains spaces or
special characters, or if it is case-sensitive
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Defining a Column Alias
When displaying the result of a query, SQL Developer normally uses the name of the selected
column as the column heading. This heading may not be descriptive and, therefore, may be difficult
to understand. You can change a column heading by using a column alias.
Specify the alias after the column in the SELECT list using blank space as a separator. By default,
alias headings appear in uppercase. If the alias contains spaces or special characters (such as # or $),
or if it is case-sensitive, enclose the alias in double quotation marks (“ ”).
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Oracle Database 11g: SQL Fundamentals I 1 - 17
Using Column Aliases
SELECT last_name AS name, commission_pct comm
FROM
employees;
…
SELECT last_name "Name" , salary*12 "Annual Salary"
FROM
employees;
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Using Column Aliases
The first example displays the names and the commission percentages of all the employees. Note that
the optional AS keyword has been used before the column alias name. The result of the query is the
same whether the AS keyword is used or not. Also, note that the SQL statement has the column
aliases, name and comm, in lowercase, whereas the result of the query displays the column headings
in uppercase. As mentioned in the previous slide, column headings appear in uppercase by default.
The second example displays the last names and annual salaries of all the employees. Because
Annual Salary contains a space, it has been enclosed in double quotation marks. Note that the
column heading in the output is exactly the same as the column alias.
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Oracle Database 11g: SQL Fundamentals I 1 - 18
Lesson Agenda
•
•
•
•
Basic SELECT Statement
Arithmetic Expressions and NULL values in SELECT
statement
Column Aliases
Use of concatenation operator, literal character strings,
alternative quote operator, and the DISTINCT keyword
DESCRIBE command
•
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Oracle Database 11g: SQL Fundamentals I 1 - 19
Concatenation Operator
A concatenation operator:
• Links columns or character strings to other columns
• Is represented by two vertical bars (||)
• Creates a resultant column that is a character expression
SELECT
FROM
last_name||job_id AS "Employees"
employees;
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Concatenation Operator
You can link columns to other columns, arithmetic expressions, or constant values to create a
character expression by using the concatenation operator (||). Columns on either side of the operator
are combined to make a single output column.
In the example, LAST_NAME and JOB_ID are concatenated, and given the alias Employees. Note
that the last name of the employee and the job code are combined to make a single output column.
The AS keyword before the alias name makes the SELECT clause easier to read.
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Null Values with the Concatenation Operator
If you concatenate a null value with a character string, the result is a character string. LAST_NAME
|| NULL results in LAST_NAME.
Note: You can also concatenate date expressions with other expressions or columns.
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Oracle Database 11g: SQL Fundamentals I 1 - 20
Literal Character Strings
•
A literal is a character, a number, or a date that is included
in the SELECT statement.
•
Date and character literal values must be enclosed within
single quotation marks.
Each character string is output once for each row returned.
•
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Literal Character Strings
A literal is a character, a number, or a date that is included in the SELECT list. It is not a column
name or a column alias. It is printed for each row returned. Literal strings of free-format text can be
included in the query result and are treated the same as a column in the SELECT list.
Date and character literals must be enclosed within single quotation marks (' '); number literals
need not be enclosed in a similar manner.
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Oracle Database 11g: SQL Fundamentals I 1 - 21
Using Literal Character Strings
SELECT last_name ||' is a '||job_id
AS "Employee Details"
FROM
employees;
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Using Literal Character Strings
The example in the slide displays the last names and job codes of all employees. The column has the
heading Employee Details. Note the spaces between the single quotation marks in the SELECT
statement. The spaces improve the readability of the output.
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In the following example, the last name and salary for each employee are concatenated with a literal,
to give the returned rows more meaning:
SELECT last_name ||': 1 Month salary = '||salary Monthly
FROM
employees;
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Oracle Database 11g: SQL Fundamentals I 1 - 22
Alternative Quote (q) Operator
•
•
•
Specify your own quotation mark delimiter.
Select any delimiter.
Increase readability and usability.
SELECT department_name || q'[ Department's Manager Id: ]'
|| manager_id
AS "Department and Manager"
FROM departments;
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Alternative Quote (q) Operator
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Many SQL statements use character literals in expressions or conditions. If the literal itself contains a
single quotation mark, you can use the quote (q) operator and select your own quotation mark
delimiter.
You can choose any convenient delimiter, single-byte or multibyte, or any of the following character
pairs: [ ], { }, ( ), or < >.
In the example shown, the string contains a single quotation mark, which is normally interpreted as a
delimiter of a character string. By using the q operator, however, brackets [] are used as the quotation
mark delimiters. The string between the brackets delimiters is interpreted as a literal character string.
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Oracle Database 11g: SQL Fundamentals I 1 - 23
Duplicate Rows
The default display of queries is all rows, including duplicate
rows.
SELECT department_id
FROM
employees;
1
…
SELECT DISTINCT department_id
FROM
employees;
2
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Duplicate Rows
Unless you indicate otherwise, SQL displays the results of a query without eliminating the duplicate
rows. The first example in the slide displays all the department numbers from the EMPLOYEES table.
Note that the department numbers are repeated.
To eliminate duplicate rows in the result, include the DISTINCT keyword in the SELECT clause
immediately after the SELECT keyword. In the second example in the slide, the EMPLOYEES table
actually contains 20 rows, but there are only seven unique department numbers in the table.
You can specify multiple columns after the DISTINCT qualifier. The DISTINCT qualifier affects
all the selected columns, and the result is every distinct combination of the columns.
SELECT
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DISTINCT department_id, job_id
employees;
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Oracle Database 11g: SQL Fundamentals I 1 - 24
Lesson Agenda
•
•
•
•
Basic SELECT statement
Arithmetic expressions and NULL values in the SELECT
statement
Column aliases
Use of concatenation operator, literal character strings,
alternative quote operator, and the DISTINCT keyword
DESCRIBE command
•
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Oracle Database 11g: SQL Fundamentals I 1 - 25
Displaying the Table Structure
•
Use the DESCRIBE command to display the structure of a
table.
Or, select the table in the Connections tree and use the
Columns tab to view the table structure.
•
DESC[RIBE] tablename
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Displaying the Table Structure
In SQL Developer, you can display the structure of a table by using the DESCRIBE command. The
command displays the column names and the data types, and it shows you whether a column must
contain data (that is, whether the column has a NOT NULL constraint).
In the syntax, table name is the name of any existing table, view, or synonym that is accessible to
the user.
Using the SQL Developer GUI interface, you can select the table in the Connections tree and use the
Columns tab to view the table structure.
Note: The DESCRIBE command is supported by both SQL*Plus and SQL Developer.
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Oracle Database 11g: SQL Fundamentals I 1 - 26
Using the DESCRIBE Command
DESCRIBE employees
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Using the DESCRIBE Command
The example in the slide displays information about the structure of the EMPLOYEES table using the
DESCRIBE command.
In the resulting display, Null indicates that the values for this column may be unknown. NOT NULL
indicates that a column must contain data. Type displays the data type for a column.
The data types are described in the following table:
Data Type
NUMBER(p,s)
VARCHAR2(s)
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DATE
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CHAR(s)
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Description
Number value having a maximum number of digits p, with s
digits to the right of the decimal point
Variable-length character value of maximum size s
Date and time value between January 1, 4712 B.C. and
December 31, A.D. 9999.
Fixed-length character value of size s
Oracle Database 11g: SQL Fundamentals I 1 - 27
Quiz
Identify the SELECT statements that execute successfully.
1.
SELECT first_name, last_name, job_id, salary*12
AS Yearly Sal
FROM
employees;
2.
SELECT first_name, last_name, job_id, salary*12
yearly sal
FROM
employees;
3.
SELECT first_name, last_name, job_id, salary AS
yearly sal
FROM
employees;
4.
SELECT first_name+last_name AS name, job_Id,
salary*12 yearly sal
FROM
employees;
Copyright © 2009, Oracle. All rights reserved.
Answer: 2, 3
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Oracle Database 11g: SQL Fundamentals I 1 - 28
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Summary
In this lesson, you should have learned how to:
• Write a SELECT statement that:
– Returns all rows and columns from a table
– Returns specified columns from a table
– Uses column aliases to display more descriptive column
headings
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM table;
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Summary
In this lesson, you should have learned how to retrieve data from a database table with the SELECT
statement.
SELECT
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*|{[DISTINCT] column [alias],...}
table;
In the syntax:
SELECT
*
DISTINCT
column|expression
alias
FROM table
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is a list of one or more columns
selects all columns
suppresses duplicates
selects the named column or the expression
gives the selected columns different headings
specifies the table containing the columns
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Oracle Database 11g: SQL Fundamentals I 1 - 29
Practice 1: Overview
This practice covers the following topics:
• Selecting all data from different tables
• Describing the structure of tables
• Performing arithmetic calculations and specifying column
names
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Practice 1: Overview
In this practice, you write simple SELECT queries. The queries cover most of the SELECT clauses
and operations that you learned in this lesson.
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Oracle Database 11g: SQL Fundamentals I 1 - 30
Practice 1
Part 1
Test your knowledge:
1. The following SELECT statement executes successfully:
SELECT last_name, job_id, salary AS Sal
FROM
employees;
True/False
2. The following SELECT statement executes successfully:
SELECT *
FROM
job_grades;
True/False
3. There are four coding errors in the following statement. Can you identify them?
SELECT
sal x 12
FROM
employee_id, last_name
ANNUAL SALARY
employees;
Part 2
Note the following points before you begin with the practices:
• Save all your lab files at the following location: D:\labs\SQL1\labs
• Enter your SQL statements in a SQL Worksheet. To save a script in SQL Developer, make sure
the required SQL worksheet is active and then from the File menu, select Save As or right-click
in the SQL Worksheet and select Save file to save your SQL statement as a
lab__.sql script. When you are modifying an existing script, make sure you
use Save As to save it with a different filename.
• To run the query, click the Execute Statement icon in the SQL Worksheet. Alternatively, you
can press [F9]. For DML and DDL statements, use the Run Script icon or press [F5].
• After you have executed the query, make sure that you do not enter your next query in the same
worksheet. Open a new worksheet.
You have been hired as a SQL programmer for Acme Corporation. Your first task is to create some
reports based on data from the Human Resources tables.
4. Your first task is to determine the structure of the DEPARTMENTS table and its contents.
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Oracle Database 11g: SQL Fundamentals I 1 - 31
Practice 1 (continued)
Part 2 (continued)
5. You need to determine the structure of the EMPLOYEES table.
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The HR department wants a query to display the last name, job ID, hire date, and employee ID for
each employee, with the employee ID appearing first. Provide an alias STARTDATE for the
HIRE_DATE column. Save your SQL statement to a file named lab_01_05.sql so that you can
dispatch this file to the HR department.
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Oracle Database 11g: SQL Fundamentals I 1 - 32
Practice 1 (continued)
Part 2 (continued)
6. Test your query in the lab_01_05.sql file to ensure that it runs correctly.
Note: After you have executed the query, make sure that you do not enter your next query in the
same worksheet. Open a new worksheet.
…
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7. The HR department wants a query to display all unique job IDs from the EMPLOYEES table.
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Oracle Database 11g: SQL Fundamentals I 1 - 33
Practice 1 (continued)
Part 3
If you have time, complete the following exercises:
8. The HR department wants more descriptive column headings for its report on employees. Copy
the statement from lab_01_05.sql to a new SQL Worksheet. Name the column headings
Emp #, Employee, Job, and Hire Date, respectively. Then run your query again.
…
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9. The HR department has requested a report of all employees and their job IDs. Display the last
name concatenated with the job ID (separated by a comma and space) and name the column
Employee and Title.
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Oracle Database 11g: SQL Fundamentals I 1 - 34
Practice 1 (continued)
Part 3 (continued)
If you want an extra challenge, complete the following exercise:
10. To familiarize yourself with the data in the EMPLOYEES table, create a query to display all the
data from that table. Separate each column output by a comma. Name the column title
THE_OUTPUT.
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Oracle Database 11g: SQL Fundamentals I 1 - 35
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Restricting and Sorting Data
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Copyright © 2009, Oracle. All rights reserved.
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Objectives
After completing this lesson, you should be able to do the
following:
• Limit the rows that are retrieved by a query
• Sort the rows that are retrieved by a query
• Use ampersand substitution to restrict and sort output at
run time
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Copyright © 2009, Oracle. All rights reserved.
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Objectives
When retrieving data from the database, you may need to do the following:
• Restrict the rows of data that are displayed
• Specify the order in which the rows are displayed
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This lesson explains the SQL statements that you use to perform the actions listed above.
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Oracle Database 11g: SQL Fundamentals I 2 - 2
Lesson Agenda
•
Limiting rows with:
– The WHERE clause
– The comparison conditions using =, <=, BETWEEN, IN, LIKE,
and NULL conditions
– Logical conditions using AND, OR, and NOT operators
•
•
Rules of precedence for operators in an expression
Sorting rows using the ORDER BY clause
•
•
Substitution variables
DEFINE and VERIFY commands
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 2 - 3
Limiting Rows Using a Selection
EMPLOYEES
…
“retrieve all
employees in
department 90”
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Limiting Rows Using a Selection
In the example in the slide, assume that you want to display all the employees in department 90. The
rows with a value of 90 in the DEPARTMENT_ID column are the only ones that are returned. This
method of restriction is the basis of the WHERE clause in SQL.
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Oracle Database 11g: SQL Fundamentals I 2 - 4
Limiting the Rows That Are Selected
•
Restrict the rows that are returned by using the WHERE
clause:
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM
table
[WHERE condition(s)];
•
The WHERE clause follows the FROM clause.
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Copyright © 2009, Oracle. All rights reserved.
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Limiting the Rows That Are Selected
You can restrict the rows that are returned from the query by using the WHERE clause. A WHERE
clause contains a condition that must be met and it directly follows the FROM clause. If the condition
is true, the row meeting the condition is returned.
In the syntax:
WHERE
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restricts the query to rows that meet a condition
is composed of column names, expressions,
constants, and a comparison operator. A condition specifies a
combination of one or more expressions and logical (Boolean)
operators, and returns a value of TRUE, FALSE, or UNKNOWN.
The WHERE clause can compare values in columns, literal, arithmetic expressions, or functions. It
consists of three elements:
• Column name
• Comparison condition
• Column name, constant, or list of values
condition
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Oracle Database 11g: SQL Fundamentals I 2 - 5
Using the WHERE Clause
SELECT employee_id, last_name, job_id, department_id
FROM
employees
WHERE department_id = 90 ;
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Using the WHERE Clause
In the example, the SELECT statement retrieves the employee ID, last name, job ID, and department
number of all employees who are in department 90.
Note: You cannot use column alias in the WHERE clause.
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Oracle Database 11g: SQL Fundamentals I 2 - 6
Character Strings and Dates
•
Character strings and date values are enclosed with single
quotation marks.
Character values are case-sensitive and date values are
format-sensitive.
The default date display format is DD-MON-RR.
•
•
SELECT last_name, job_id, department_id
FROM
employees
WHERE last_name = 'Whalen' ;
SELECT last_name
FROM
employees
WHERE hire_date = '17-FEB-96' ;
Copyright © 2009, Oracle. All rights reserved.
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Character Strings and Dates
Character strings and dates in the WHERE clause must be enclosed with single quotation marks ('').
Number constants, however, should not be enclosed with single quotation marks.
All character searches are case-sensitive. In the following example, no rows are returned because the
EMPLOYEES table stores all the last names in mixed case:
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SELECT last_name, job_id, department_id
FROM
employees
WHERE last_name = 'WHALEN';
Oracle databases store dates in an internal numeric format, representing the century, year, month,
day, hours, minutes, and seconds. The default date display is in the DD-MON-RR format.
Note: For details about the RR format and about changing the default date format, see the lesson
titled “Using Single-Row Functions to Customize Output.” Also, you learn about the use of singlerow functions such as UPPER and LOWER to override the case sensitivity in the same lesson.
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Oracle Database 11g: SQL Fundamentals I 2 - 7
Comparison Operators
Operator
Meaning
=
Equal to
>
Greater than
>=
Greater than or equal to
<
Less than
<=
Less than or equal to
<>
Not equal to
BETWEEN
...AND...
Between two values (inclusive)
IN(set)
Match any of a list of values
LIKE
Match a character pattern
IS NULL
Is a null value
Copyright © 2009, Oracle. All rights reserved.
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Comparison Operators
Comparison operators are used in conditions that compare one expression to another value or
expression. They are used in the WHERE clause in the following format:
Syntax
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... WHERE expr operator value
Example
... WHERE hire_date = '01-JAN-95'
... WHERE salary >= 6000
... WHERE last_name = 'Smith'
An alias cannot be used in the WHERE clause.
Note: The symbols != and ^= can also represent the not equal to condition.
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Oracle Database 11g: SQL Fundamentals I 2 - 8
Using Comparison Operators
SELECT last_name, salary
FROM
employees
WHERE salary <= 3000 ;
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Using Comparison Operators
In the example, the SELECT statement retrieves the last name and salary from the EMPLOYEES
table for any employee whose salary is less than or equal to $3,000. Note that there is an explicit
value supplied to the WHERE clause. The explicit value of 3000 is compared to the salary value in
the SALARY column of the EMPLOYEES table.
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Oracle Database 11g: SQL Fundamentals I 2 - 9
Range Conditions Using the BETWEEN Operator
Use the BETWEEN operator to display rows based on a range of
values:
SELECT last_name, salary
FROM
employees
WHERE salary BETWEEN 2500 AND 3500 ;
Lower limit
Upper limit
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Copyright © 2009, Oracle. All rights reserved.
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Range Conditions Using the BETWEEN Operator
You can display rows based on a range of values using the BETWEEN operator. The range that you
specify contains a lower limit and an upper limit.
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The SELECT statement in the slide returns rows from the EMPLOYEES table for any employee
whose salary is between $2,500 and $3,500.
Values that are specified with the BETWEEN operator are inclusive. However, you must specify the
lower limit first.
You can also use the BETWEEN operator on character values:
SELECT last_name
FROM
employees
WHERE last_name BETWEEN 'King' AND 'Smith';
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Oracle Database 11g: SQL Fundamentals I 2 - 10
Membership Condition Using the IN Operator
Use the IN operator to test for values in a list:
SELECT employee_id, last_name, salary, manager_id
FROM
employees
WHERE manager_id IN (100, 101, 201) ;
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Copyright © 2009, Oracle. All rights reserved.
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Membership Condition Using the IN Operator
To test for values in a specified set of values, use the IN operator. The condition defined using the
IN operator is also known as the membership condition.
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The slide example displays employee numbers, last names, salaries, and managers’ employee
numbers for all the employees whose manager’s employee number is 100, 101, or 201.
The IN operator can be used with any data type. The following example returns a row from the
EMPLOYEES table, for any employee whose last name is included in the list of names in the WHERE
clause:
SELECT employee_id, manager_id, department_id
FROM
employees
WHERE last_name IN ('Hartstein', 'Vargas');
If characters or dates are used in the list, they must be enclosed with single quotation marks ('').
Note: The IN operator is internally evaluated by the Oracle server as a set of OR conditions, such as
a=value1 or a=value2 or a=value3. Therefore, using the IN operator has no performance
benefits and is used only for logical simplicity.
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Oracle Database 11g: SQL Fundamentals I 2 - 11
Pattern Matching Using the LIKE Operator
•
Use the LIKE operator to perform wildcard searches of
valid search string values.
Search conditions can contain either literal characters or
numbers:
•
– % denotes zero or many characters.
– _ denotes one character.
SELECT
FROM
WHERE
first_name
employees
first_name LIKE 'S%' ;
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Copyright © 2009, Oracle. All rights reserved.
Pattern Matching Using the LIKE Operator
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You may not always know the exact value to search for. You can select rows that match a character
pattern by using the LIKE operator. The character pattern–matching operation is referred to as a
wildcard search. Two symbols can be used to construct the search string.
Symbol
Description
Represents any sequence of zero or more characters
%
Represents any single character
_
The SELECT statement in the slide returns the first name from the EMPLOYEES table for any
employee whose first name begins with the letter “S.” Note the uppercase “S.” Consequently, names
beginning with a lowercase “s” are not returned.
The LIKE operator can be used as a shortcut for some BETWEEN comparisons. The following
example displays the last names and hire dates of all employees who joined between January, 1995
and December, 1995:
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SELECT last_name, hire_date
FROM
employees
WHERE hire_date LIKE '%95';
Oracle Database 11g: SQL Fundamentals I 2 - 12
Combining Wildcard Characters
•
You can combine the two wildcard characters (%, _) with
literal characters for pattern matching:
SELECT last_name
FROM
employees
WHERE last_name LIKE '_o%' ;
•
You can use the ESCAPE identifier to search for the actual
% and _ symbols.
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Copyright © 2009, Oracle. All rights reserved.
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Combining Wildcard Characters
The % and _ symbols can be used in any combination with literal characters. The example in the slide
displays the names of all employees whose last names have the letter “o” as the second character.
ESCAPE Identifier
When you need to have an exact match for the actual % and _ characters, use the ESCAPE identifier.
This option specifies what the escape character is. If you want to search for strings that contain SA_,
you can use the following SQL statement:
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SELECT employee_id, last_name, job_id
FROM
employees WHERE job_id LIKE '%SA\_%' ESCAPE '\';
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The ESCAPE identifier identifies the backslash (\) as the escape character. In the SQL statement, the
escape character precedes the underscore (_). This causes the Oracle server to interpret the
underscore literally.
Oracle Database 11g: SQL Fundamentals I 2 - 13
Using the NULL Conditions
Test for nulls with the IS NULL operator.
SELECT last_name, manager_id
FROM
employees
WHERE manager_id IS NULL ;
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Using the NULL Conditions
The NULL conditions include the IS NULL condition and the IS NOT NULL condition.
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The IS NULL condition tests for nulls. A null value means that the value is unavailable, unassigned,
unknown, or inapplicable. Therefore, you cannot test with =, because a null cannot be equal or
unequal to any value. The slide example retrieves the last names and managers of all employees who
do not have a manager.
Here is another example: To display the last name, job ID, and commission for all employees who
are not entitled to receive a commission, use the following SQL statement:
SELECT last_name, job_id, commission_pct
FROM
employees
WHERE commission_pct IS NULL;
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Oracle Database 11g: SQL Fundamentals I 2 - 14
Defining Conditions Using the Logical Operators
Operator
Meaning
AND
Returns TRUE if both component conditions
are true
OR
Returns TRUE if either component condition
is true
NOT
Returns TRUE if the condition is false
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Defining Conditions Using the Logical Operators
A logical condition combines the result of two component conditions to produce a single result based
on those conditions or it inverts the result of a single condition. A row is returned only if the overall
result of the condition is true.
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Three logical operators are available in SQL:
• AND
• OR
• NOT
All the examples so far have specified only one condition in the WHERE clause. You can use several
conditions in a single WHERE clause using the AND and OR operators.
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Oracle Database 11g: SQL Fundamentals I 2 - 15
Using the AND Operator
AND requires both the component conditions to be true:
SELECT
FROM
WHERE
AND
employee_id, last_name, job_id, salary
employees
salary >= 10000
job_id LIKE '%MAN%' ;
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Copyright © 2009, Oracle. All rights reserved.
Using the AND Operator
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In the example, both the component conditions must be true for any record to be selected. Therefore,
only those employees who have a job title that contains the string ‘MAN’ and earn $10,000 or more
are selected.
All character searches are case-sensitive, that is no rows are returned if ‘MAN’ is not uppercase.
Further, character strings must be enclosed with quotation marks.
AND Truth Table
The following table shows the results of combining two expressions with AND:
AND
TRUE
FALSE
NULL
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TRUE
TRUE
FALSE
NULL
FALSE
FALSE
FALSE
FALSE
NULL
NULL
FALSE
NULL
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Oracle Database 11g: SQL Fundamentals I 2 - 16
Using the OR Operator
OR requires either component condition to be true:
SELECT
FROM
WHERE
OR
employee_id, last_name, job_id, salary
employees
salary >= 10000
job_id LIKE '%MAN%' ;
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Copyright © 2009, Oracle. All rights reserved.
Using the OR Operator
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In the example, either component condition can be true for any record to be selected. Therefore, any
employee who has a job ID that contains the string ‘MAN’ or earns $10,000 or more is selected.
OR Truth Table
The following table shows the results of combining two expressions with OR:
OR
TRUE
FALSE
NULL
TRUE
TRUE
TRUE
TRUE
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TRUE
FALSE
NULL
NULL
TRUE
NULL
NULL
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Oracle Database 11g: SQL Fundamentals I 2 - 17
Using the NOT Operator
SELECT last_name, job_id
FROM
employees
WHERE job_id
NOT IN ('IT_PROG', 'ST_CLERK', 'SA_REP') ;
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Using the NOT Operator
The slide example displays the last name and job ID of all employees whose job ID is not IT_PROG,
ST_CLERK, or SA_REP.
NOT Truth Table
The following table shows the result of applying the NOT operator to a condition:
NOT
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TRUE
FALSE
FALSE
TRUE
NULL
NULL
Note: The NOT operator can also be used with other SQL operators, such as BETWEEN, LIKE, and
NULL.
...
...
...
...
WHERE
WHERE
WHERE
WHERE
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job_id
NOT IN ('AC_ACCOUNT', 'AD_VP')
salary
NOT BETWEEN 10000 AND 15000
last_name NOT LIKE '%A%'
commission_pct IS
NOT NULL
Oracle Database 11g: SQL Fundamentals I 2 - 18
Lesson Agenda
•
Limiting rows with:
– The WHERE clause
– The comparison conditions using =, <=, BETWEEN, IN, LIKE,
and NULL operators
– Logical conditions using AND, OR, and NOT operators
•
•
Rules of precedence for operators in an expression
Sorting rows using the ORDER BY clause
•
•
Substitution variables
DEFINE and VERIFY commands
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 2 - 19
Rules of Precedence
Operator
Meaning
1
Arithmetic operators
2
Concatenation operator
3
Comparison conditions
4
IS [NOT] NULL, LIKE, [NOT] IN
5
[NOT] BETWEEN
6
Not equal to
7
NOT logical condition
8
AND logical condition
9
OR logical condition
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You can use parentheses to override rules of precedence.
Copyright © 2009, Oracle. All rights reserved.
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Rules of Precedence
The rules of precedence determine the order in which expressions are evaluated and calculated. The
table in the slide lists the default order of precedence. However, you can override the default order by
using parentheses around the expressions that you want to calculate first.
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Oracle Database 11g: SQL Fundamentals I 2 - 20
Rules of Precedence
SELECT
FROM
WHERE
OR
AND
last_name, job_id, salary
employees
job_id = 'SA_REP'
job_id = 'AD_PRES'
salary > 15000;
SELECT
FROM
WHERE
OR
AND
last_name, job_id, salary
employees
(job_id = 'SA_REP'
job_id = 'AD_PRES')
salary > 15000;
Copyright © 2009, Oracle. All rights reserved.
Rules of Precedence (continued)
1. Precedence of the AND Operator: Example
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1
2
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In this example, there are two conditions:
• The first condition is that the job ID is AD_PRES and the salary is greater than $15,000.
• The second condition is that the job ID is SA_REP.
Therefore, the SELECT statement reads as follows:
“Select the row if an employee is a president and earns more than $15,000, or if the employee is a
sales representative.”
2. Using Parentheses: Example
In this example, there are two conditions:
• The first condition is that the job ID is AD_PRES or SA_REP.
• The second condition is that the salary is greater than $15,000.
Therefore, the SELECT statement reads as follows:
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“Select the row if an employee is a president or a sales representative, and if the employee earns
more than $15,000.”
Oracle Database 11g: SQL Fundamentals I 2 - 21
Lesson Agenda
•
Limiting rows with:
– The WHERE clause
– The comparison conditions using =, <=, BETWEEN, IN, LIKE,
and NULL operators
– Logical conditions using AND, OR, and NOT operators
•
•
Rules of precedence for operators in an expression
Sorting rows using the ORDER BY clause
•
•
Substitution variables
DEFINE and VERIFY commands
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 2 - 22
Using the ORDER BY Clause
•
Sort retrieved rows with the ORDER BY clause:
– ASC: Ascending order, default
– DESC: Descending order
•
The ORDER BY clause comes last in the SELECT
statement:
SELECT
last_name, job_id, department_id, hire_date
FROM
employees
ORDER BY hire_date ;
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Copyright © 2009, Oracle. All rights reserved.
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Using the ORDER BY Clause
The order of rows that are returned in a query result is undefined. The ORDER BY clause can be used
to sort the rows. However, if you use the ORDER BY clause, it must be the last clause of the SQL
statement. Further, you can specify an expression, an alias, or a column position as the sort condition.
Syntax
SELECT
FROM
[WHERE
[ORDER BY
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expr
table
condition(s)]
{column, expr, numeric_position} [ASC|DESC]];
In the syntax:
ORDER BY
specifies the order in which the retrieved rows are displayed
ASC
orders the rows in ascending order (this is the default order)
DESC
orders the rows in descending order
If the ORDER BY clause is not used, the sort order is undefined, and the Oracle server may not fetch
rows in the same order for the same query twice. Use the ORDER BY clause to display the rows in a
specific order.
Note: Use the keywords NULLS FIRST or NULLS LAST to specify whether returned rows
containing null values should appear first or last in the ordering sequence.
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Oracle Database 11g: SQL Fundamentals I 2 - 23
Sorting
•
Sorting in descending order:
SELECT
last_name, job_id, department_id, hire_date
FROM
employees
1
ORDER BY hire_date DESC ;
•
Sorting by column alias:
SELECT employee_id, last_name, salary*12 annsal
FROM
employees
ORDER BY annsal ;
2
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Sorting
The default sort order is ascending:
• Numeric values are displayed with the lowest values first (for example, 1 to 999).
• Date values are displayed with the earliest value first (for example, 01-JAN-92 before
01-JAN-95).
• Character values are displayed in the alphabetical order (for example, “A” first and “Z” last).
• Null values are displayed last for ascending sequences and first for descending sequences.
• You can also sort by a column that is not in the SELECT list.
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Examples:
1. To reverse the order in which the rows are displayed, specify the DESC keyword after the
column name in the ORDER BY clause. The slide example sorts the result by the most recently
hired employee.
2. You can also use a column alias in the ORDER BY clause. The slide example sorts the data by
annual salary.
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Oracle Database 11g: SQL Fundamentals I 2 - 24
Sorting
•
Sorting by using the column’s numeric position:
SELECT
last_name, job_id, department_id, hire_date
FROM
employees
3
ORDER BY 3;
•
Sorting by multiple columns:
SELECT last_name, department_id, salary
FROM
employees
ORDER BY department_id, salary DESC;
4
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Sorting (continued)
Examples:
3. You can sort query results by specifying the numeric position of the column in the SELECT
clause. The slide example sorts the result by the department_id as this column is at the
third position in the SELECT clause.
4. You can sort query results by more than one column. The sort limit is the number of columns in
the given table. In the ORDER BY clause, specify the columns and separate the column names
using commas. If you want to reverse the order of a column, specify DESC after its name.
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Oracle Database 11g: SQL Fundamentals I 2 - 25
Lesson Agenda
•
Limiting rows with:
– The WHERE clause
– The comparison conditions using =, <=, BETWEEN, IN, LIKE,
and NULL operators
– Logical conditions using AND, OR, and NOT operators
•
•
Rules of precedence for operators in an expression
Sorting rows using the ORDER BY clause
•
•
Substitution variables
DEFINE and VERIFY commands
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Oracle Database 11g: SQL Fundamentals I 2 - 26
Substitution Variables
... salary = ? …
… department_id = ? …
... last_name = ? ...
I want
to query
different
values.
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Substitution Variables
So far, all the SQL statements were executed with predetermined columns, conditions and their
values. Suppose that you want a query that lists the employees with various jobs and not just those
whose job_ID is SA_REP. You can edit the WHERE clause to provide a different value each time
you run the command, but there is also an easier way.
By using a substitution variable in place of the exact values in the WHERE clause, you can run the
same query for different values.
You can create reports that prompt users to supply their own values to restrict the range of data
returned, by using substitution variables. You can embed substitution variables in a command file or
in a single SQL statement. A variable can be thought of as a container in which values are
temporarily stored. When the statement is run, the stored value is substituted.
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Oracle Database 11g: SQL Fundamentals I 2 - 27
Substitution Variables
•
Use substitution variables to:
– Temporarily store values with single-ampersand (&) and
double-ampersand (&&) substitution
•
Use substitution variables to supplement the following:
– WHERE conditions
– ORDER BY clauses
– Column expressions
– Table names
– Entire SELECT statements
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Substitution Variables (continued)
You can use single-ampersand (&) substitution variables to temporarily store values.
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You can also predefine variables by using the DEFINE command. DEFINE creates and assigns a
value to a variable.
Restricted Ranges of Data: Examples
• Reporting figures only for the current quarter or specified date range
• Reporting on data relevant only to the user requesting the report
• Displaying personnel only within a given department
Other Interactive Effects
Interactive effects are not restricted to direct user interaction with the WHERE clause. The same
principles can also be used to achieve other goals, such as:
• Obtaining input values from a file rather than from a person
• Passing values from one SQL statement to another
Note: Both SQL Developer and SQL* Plus support substitution variables and the
DEFINE/UNDEFINE commands. Neither SQL Developer nor SQL* Plus support validation checks
(except for data type) on user input. If used in scripts that are deployed to users, substitution variables
can be subverted for SQL injection attacks.
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Oracle Database 11g: SQL Fundamentals I 2 - 28
Using the Single-Ampersand Substitution
Variable
Use a variable prefixed with an ampersand (&) to prompt the
user for a value:
SELECT employee_id, last_name, salary, department_id
FROM
employees
WHERE employee_id = &employee_num ;
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Using the Single-Ampersand Substitution Variable
When running a report, users often want to restrict the data that is returned dynamically. SQL*Plus
or SQL Developer provides this flexibility with user variables. Use an ampersand (&) to identify each
variable in your SQL statement. However, you do not need to define the value of each variable.
Notation
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Description
&user_variable
Indicates a variable in a SQL statem ent; if the variable
does not exist, SQL*Plus or SQL Developer prom pts the
user for a value (the new variable is discarded after it is
used.)
The example in the slide creates a SQL Developer substitution variable for an employee number.
When the statement is executed, SQL Developer prompts the user for an employee number and then
displays the employee number, last name, salary, and department number for that employee.
With the single ampersand, the user is prompted every time the command is executed if the variable
does not exist.
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Oracle Database 11g: SQL Fundamentals I 2 - 29
Using the Single-Ampersand Substitution
Variable
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Using the Single-Ampersand Substitution Variable (continued)
When SQL Developer detects that the SQL statement contains an ampersand, you are prompted to
enter a value for the substitution variable that is named in the SQL statement.
After you enter a value and click the OK button, the results are displayed in the Results tab of your
SQL Developer session.
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Oracle Database 11g: SQL Fundamentals I 2 - 30
Character and Date Values with
Substitution Variables
Use single quotation marks for date and character values:
SELECT last_name, department_id, salary*12
FROM
employees
WHERE job_id = '&job_title' ;
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Character and Date Values with Substitution Variables
In a WHERE clause, date and character values must be enclosed with single quotation marks. The
same rule applies to the substitution variables.
Enclose the variable with single quotation marks within the SQL statement itself.
The slide shows a query to retrieve the employee names, department numbers, and annual salaries of
all employees based on the job title value of the SQL Developer substitution variable.
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Oracle Database 11g: SQL Fundamentals I 2 - 31
Specifying Column Names,
Expressions, and Text
SELECT employee_id, last_name, job_id,&column_name
FROM
employees
WHERE &condition
ORDER BY &order_column ;
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Specifying Column Names, Expressions, and Text
You can use the substitution variables not only in the WHERE clause of a SQL statement, but also as
substitution for column names, expressions, or text.
Example:
The slide example displays the employee number, last name, job title, and any other column that is
specified by the user at run time, from the EMPLOYEES table. For each substitution variable in the
SELECT statement, you are prompted to enter a value, and then click OK to proceed.
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If you do not enter a value for the substitution variable, you get an error when you execute the
preceding statement.
Note: A substitution variable can be used anywhere in the SELECT statement, except as the first
word entered at the command prompt.
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Oracle Database 11g: SQL Fundamentals I 2 - 32
Using the Double-Ampersand
Substitution Variable
Use double ampersand (&&) if you want to reuse the variable
value without prompting the user each time:
SELECT
employee_id, last_name, job_id, &&column_name
FROM
employees
ORDER BY &column_name ;
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…
Copyright © 2009, Oracle. All rights reserved.
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Using the Double-Ampersand Substitution Variable
You can use the double-ampersand (&&) substitution variable if you want to reuse the variable value
without prompting the user each time. The user sees the prompt for the value only once. In the
example in the slide, the user is asked to give the value for the variable, column_name, only once.
The value that is supplied by the user (department_id) is used for both display and ordering of
data. If you run the query again, you will not be prompted for the value of the variable.
SQL Developer stores the value that is supplied by using the DEFINE command; it uses it again
whenever you reference the variable name. After a user variable is in place, you need to use the
UNDEFINE command to delete it:
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UNDEFINE column_name
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Oracle Database 11g: SQL Fundamentals I 2 - 33
Lesson Agenda
•
Limiting rows with:
– The WHERE clause
– The comparison conditions using =, <=, BETWEEN, IN, LIKE,
and NULL operators
– Logical conditions using AND, OR, and NOT operators
•
•
Rules of precedence for operators in an expression
Sorting rows using the ORDER BY clause
•
•
Substitution variables
DEFINE and VERIFY commands
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Oracle Database 11g: SQL Fundamentals I 2 - 34
Using the DEFINE Command
•
Use the DEFINE command to create and assign a value to
a variable.
Use the UNDEFINE command to remove a variable.
•
DEFINE employee_num = 200
SELECT employee_id, last_name, salary, department_id
FROM
employees
WHERE employee_id = &employee_num ;
UNDEFINE employee_num
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Using the DEFINE Command
The example shown creates a substitution variable for an employee number by using the DEFINE
command. At run time, this displays the employee number, name, salary, and department number for
that employee.
Because the variable is created using the SQL Developer DEFINE command, the user is not
prompted to enter a value for the employee number. Instead, the defined variable value is
automatically substituted in the SELECT statement.
The EMPLOYEE_NUM substitution variable is present in the session until the user undefines it or
exits the SQL Developer session.
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Oracle Database 11g: SQL Fundamentals I 2 - 35
Using the VERIFY Command
Use the VERIFY command to toggle the display of the
substitution variable, both before and after SQL Developer
replaces substitution variables with values:
SET VERIFY ON
SELECT employee_id, last_name, salary
FROM
employees
WHERE employee_id = &employee_num;
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Using the VERIFY Command
To confirm the changes in the SQL statement, use the VERIFY command. Setting SET VERIFY ON
forces SQL Developer to display the text of a command after it replaces substitution variables with
values. To see the VERIFY output, you should use the Run Script (F5) icon in the SQL Worksheet.
SQL Developer displays the text of a command after it replaces substitution variables with values, in
the Script Output tab as shown in the slide.
The example in the slide displays the new value of the EMPLOYEE_ID column in the SQL statement
followed by the output.
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SQL*Plus System Variables
SQL*Plus uses various system variables that control the working environment. One of the variables
is VERIFY. To obtain a complete list of all the system variables, you can issue the SHOW ALL
command on the SQL*Plus command prompt.
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Oracle Database 11g: SQL Fundamentals I 2 - 36
Quiz
Which of the following are valid operators for the WHERE
clause?
1. >=
2. IS NULL
3. !=
4. IS LIKE
5. IN BETWEEN
6. <>
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Copyright © 2009, Oracle. All rights reserved.
Answer: 1, 2, 3, 6
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Oracle Database 11g: SQL Fundamentals I 2 - 37
Summary
In this lesson, you should have learned how to:
• Use the WHERE clause to restrict rows of output:
– Use the comparison conditions
– Use the BETWEEN, IN, LIKE, and NULL operators
– Apply the logical AND, OR, and NOT operators
•
Use the ORDER BY clause to sort rows of output:
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM
table
[WHERE condition(s)]
[ORDER BY {column, expr, alias} [ASC|DESC]] ;
•
Use ampersand substitution to restrict and sort output at
run time
Copyright © 2009, Oracle. All rights reserved.
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Summary
In this lesson, you should have learned about restricting and sorting rows that are returned by the
SELECT statement. You should also have learned how to implement various operators and
conditions.
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By using the substitution variables, you can add flexibility to your SQL statements. This enables the
queries to prompt for the filter condition for the rows during run time.
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Oracle Database 11g: SQL Fundamentals I 2 - 38
Practice 2: Overview
This practice covers the following topics:
• Selecting data and changing the order of the rows
that are displayed
• Restricting rows by using the WHERE clause
• Sorting rows by using the ORDER BY clause
•
Using substitution variables to add flexibility to your
SQL SELECT statements
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Practice 2: Overview
In this practice, you build more reports, including statements that use the WHERE clause and the
ORDER BY clause. You make the SQL statements more reusable and generic by including the
ampersand substitution.
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Oracle Database 11g: SQL Fundamentals I 2 - 39
Practice 2
The HR department needs your assistance in creating some queries.
1. Because of budget issues, the HR department needs a report that displays the last name and
salary of employees who earn more than $12,000. Save your SQL statement as a file named
lab_02_01.sql. Run your query.
2. Open a new SQL Worksheet. Create a report that displays the last name and department number
for employee number 176. Run the query.
3. The HR department needs to find high-salary and low-salary employees. Modify
lab_02_01.sql to display the last name and salary for any employee whose salary is not in
the range of $5,000 to $12,000. Save your SQL statement as lab_02_03.sql.
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Oracle Database 11g: SQL Fundamentals I 2 - 40
Practice 2 (continued)
4. Create a report to display the last name, job ID, and hire date for employees with the last names
of Matos and Taylor. Order the query in ascending order by the hire date.
5. Display the last name and department ID of all employees in departments 20 or 50 in ascending
alphabetical order by name.
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6. Modify lab_02_03.sql to display the last name and salary of employees who earn between
$5,000 and $12,000, and are in department 20 or 50. Label the columns Employee and
Monthly Salary, respectively. Resave lab_02_03.sql as lab_02_06.sql. Run the
statement in lab_02_06.sql.
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Oracle Database 11g: SQL Fundamentals I 2 - 41
Practice 2 (continued)
7. The HR department needs a report that displays the last name and hire date for all employees
who were hired in 1994.
8. Create a report to display the last name and job title of all employees who do not have a
manager.
9. Create a report to display the last name, salary, and commission of all employees who earn
commissions. Sort data in descending order of salary and commissions.
Use the column’s numeric position in the ORDER BY clause.
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10. Members of the HR department want to have more flexibility with the queries that you are
writing. They would like a report that displays the last name and salary of employees who earn
more than an amount that the user specifies after a prompt. Save this query to a file named
lab_02_10.sql. If you enter 12000 when prompted, the report displays the following
results:
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Oracle Database 11g: SQL Fundamentals I 2 - 42
Practice 2 (continued)
11. The HR department wants to run reports based on a manager. Create a query that prompts the
user for a manager ID and generates the employee ID, last name, salary, and department for
that manager’s employees. The HR department wants the ability to sort the report on a selected
column. You can test the data with the following values:
manager_id = 103, sorted by last_name:
manager_id = 201, sorted by salary:
manager_id = 124, sorted by employee_id:
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Oracle Database 11g: SQL Fundamentals I 2 - 43
Practice 2 (continued)
If you have time, complete the following exercises:
12. Display all employee last names in which the third letter of the name is “a.”
13. Display the last names of all employees who have both an “a” and an “e” in their last name.
If you want an extra challenge, complete the following exercises:
14. Display the last name, job, and salary for all employees whose jobs are either those of a sales
representative or of a stock clerk, and whose salaries are not equal to $2,500, $3,500, or $7,000.
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15. Modify lab_02_06.sql to display the last name, salary, and commission for all employees
whose commission is 20%. Resave lab_02_06.sql as lab_02_15.sql. Rerun the
statement in lab_02_15.sql.
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Oracle Database 11g: SQL Fundamentals I 2 - 44
Using Single-Row Functions to
Customize Output
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Objectives
After completing this lesson, you should be able to do the
following:
• Describe various types of functions available in SQL
• Use character, number, and date functions in SELECT
statements
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Objectives
Functions make the basic query block more powerful, and they are used to manipulate data values.
This is the first of two lessons that explore functions. It focuses on single-row character, number, and
date functions.
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Oracle Database 11g: SQL Fundamentals I 3 - 2
Lesson Agenda
•
•
•
•
•
Single-row SQL functions
Character functions
Number functions
Working with dates
Date functions
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Oracle Database 11g: SQL Fundamentals I 3 - 3
SQL Functions
Output
Input
Function
Function performs
action
arg 1
arg 2
Result
value
arg n
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SQL Functions
Functions are a very powerful feature of SQL. They can be used to do the following:
• Perform calculations on data
• Modify individual data items
• Manipulate output for groups of rows
• Format dates and numbers for display
• Convert column data types
SQL functions sometimes take arguments and always return a value.
Note: If you want to know whether a function is a SQL:2003 compliant function, refer to the Oracle
Compliance To Core SQL:2003 section in Oracle Database SQL Language Reference 11g, Release 1
(11.1).
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Oracle Database 11g: SQL Fundamentals I 3 - 4
Two Types of SQL Functions
Functions
Single-row
functions
Multiple-row
functions
Return one result
per row
Return one result
per set of rows
Copyright © 2009, Oracle. All rights reserved.
Two Types of SQL Functions
There are two types of functions:
• Single-row functions
• Multiple-row functions
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Single-Row Functions
These functions operate on single rows only and return one result per row. There are different types
of single-row functions. This lesson covers the following ones:
• Character
• Number
• Date
• Conversion
• General
Multiple-Row Functions
Functions can manipulate groups of rows to give one result per group of rows. These functions are
also known as group functions (covered in lesson 5 titled “Reporting Aggregated Data Using the
Group Functions”).
Note: For more information and a complete list of available functions and their syntax, see the topic,
Functions in Oracle Database SQL Language Reference 11g, Release 1 (11.1).
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Oracle Database 11g: SQL Fundamentals I 3 - 5
Single-Row Functions
Single-row functions:
• Manipulate data items
• Accept arguments and return one value
• Act on each row that is returned
• Return one result per row
• May modify the data type
• Can be nested
• Accept arguments that can be a column or an expression
function_name [(arg1, arg2,...)]
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Single-Row Functions
Single-row functions are used to manipulate data items. They accept one or more arguments and
return one value for each row that is returned by the query. An argument can be one of the following:
• User-supplied constant
• Variable value
• Column name
• Expression
Features of single-row functions include:
• Acting on each row that is returned in the query
• Returning one result per row
• Possibly returning a data value of a different type than the one that is referenced
• Possibly expecting one or more arguments
• Can be used in SELECT, WHERE, and ORDER BY clauses; can be nested
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In the syntax:
function_name
arg1, arg2
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is the name of the function
is any argument to be used by the function. This can be
represented by a column name or expression.
Oracle Database 11g: SQL Fundamentals I 3 - 6
Single-Row Functions
Character
Single-row
functions
General
Conversion
Number
Date
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Single-Row Functions (continued)
This lesson covers the following single-row functions:
• Character functions: Αccept character input and can return both character and number values
• Number functions: Accept numeric input and return numeric values
• Date functions: Operate on values of the DATE data type (All date functions return a value of
the DATE data type except the MONTHS_BETWEEN function, which returns a number.)
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The following single-row functions are discussed in the next lesson titled “Using Conversion
Functions and Conditional Expressions”:
• Conversion functions: Convert a value from one data type to another
• General functions:
- NVL
- NVL2
- NULLIF
- COALESCE
- CASE
- DECODE
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Oracle Database 11g: SQL Fundamentals I 3 - 7
Lesson Agenda
•
•
•
•
•
Single-row SQL functions
Character functions
Number functions
Working with dates
Date functions
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Oracle Database 11g: SQL Fundamentals I 3 - 8
Character Functions
Character
functions
Case-conversion
functions
Character-manipulation
functions
LOWER
UPPER
INITCAP
CONCAT
SUBSTR
LENGTH
INSTR
LPAD | RPAD
TRIM
REPLACE
Copyright © 2009, Oracle. All rights reserved.
Character Functions
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Single-row character functions accept character data as input and can return both character and
numeric values. Character functions can be divided into the following:
• Case-conversion functions
• Character-manipulation functions
Function
Purpose
LOWER(column|expression)
Converts alpha character values to lowercase
UPPER(column|expression)
Converts alpha character values to uppercase
INITCAP(column|expression)
Converts alpha character values to uppercase for the first
letter of each word; all other letters in lowercase
CONCAT(column1|expression1,
column2|expression2)
Concatenates the first character value to the second
character value; equivalent to concatenation operator (||)
SUBSTR(column|expression,m[
,n])
Returns specified characters from character value starting at
character position m, n characters long (If m is negative, the
count starts from the end of the character value. If n is
omitted, all characters to the end of the string are returned.)
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Note: The functions discussed in this lesson are only some of the available functions.
Oracle Database 11g: SQL Fundamentals I 3 - 9
Character Functions (continued)
Function
Purpose
LENGTH(column|expression)
Returns the number of characters in the expression
INSTR(column|expression,
’string’, [,m], [n] )
Returns the numeric position of a named string.
Optionally, you can provide a position m to start
searching, and the occurrence n of the string. m and n
default to 1, meaning start the search at the beginning
of the string and report the first occurrence.
Returns an expression left-padded to length of n
characters with a character expression.
Returns an expression right-padded to length of n
characters with a character expression.
LPAD(column|expression, n,
'string')
RPAD(column|expression, n,
'string')
TRIM(leading|trailing|both, Enables you to trim leading or trailing characters (or
trim_character FROM
both) from a character string. If trim_character or
trim_source)
trim_source is a character literal, you must enclose it in
single quotation marks.
This is a feature that is available in Oracle8i and later
versions.
REPLACE(text,
search_string,
replacement_string)
Searches a text expression for a character string and, if
found, replaces it with a specified replacement string
Note: Some of the functions that are fully or partially SQL:2003 compliant are:
UPPER
LOWER
TRIM
LENGTH
SUBSTR
INSTR
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Refer to the Oracle Compliance To Core SQL:2003 section in Oracle Database SQL Language
Reference 11g, Release 1 (11.1) for more information.
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Oracle Database 11g: SQL Fundamentals I 3 - 10
Case-Conversion Functions
These functions convert the case for character strings:
Function
Result
LOWER('SQL Course')
sql course
UPPER('SQL Course')
SQL COURSE
INITCAP('SQL Course')
Sql Course
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Case-Conversion Functions
LOWER, UPPER, and INITCAP are the three case-conversion functions.
• LOWER: Converts mixed-case or uppercase character strings to lowercase
• UPPER: Converts mixed-case or lowercase character strings to uppercase
• INITCAP: Converts the first letter of each word to uppercase and the remaining letters to
lowercase
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SELECT 'The job id for '||UPPER(last_name)||' is '
||LOWER(job_id) AS "EMPLOYEE DETAILS"
FROM
employees;
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Oracle Database 11g: SQL Fundamentals I 3 - 11
Using Case-Conversion Functions
Display the employee number, name, and department number
for employee Higgins:
SELECT employee_id, last_name, department_id
FROM
employees
WHERE last_name = 'higgins';
SELECT employee_id, last_name, department_id
FROM
employees
WHERE LOWER(last_name) = 'higgins';
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Using Case-Conversion Functions
The slide example displays the employee number, name, and department number of employee
Higgins.
The WHERE clause of the first SQL statement specifies the employee name as higgins. Because all
the data in the EMPLOYEES table is stored in proper case, the name higgins does not find a match
in the table, and no rows are selected.
The WHERE clause of the second SQL statement specifies that the employee name in the
EMPLOYEES table is compared to higgins, converting the LAST_NAME column to lowercase for
comparison purposes. Because both names are now lowercase, a match is found and one row is
selected. The WHERE clause can be rewritten in the following manner to produce the same result:
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...WHERE last_name = 'Higgins'
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The name in the output appears as it was stored in the database. To display the name in uppercase,
use the UPPER function in the SELECT statement.
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SELECT employee_id, UPPER(last_name), department_id
FROM
employees
WHERE INITCAP(last_name) = 'Higgins';
Oracle Database 11g: SQL Fundamentals I 3 - 12
Character-Manipulation Functions
These functions manipulate character strings:
Function
Result
CONCAT('Hello', 'World')
HelloWorld
SUBSTR('HelloWorld',1,5)
Hello
LENGTH('HelloWorld')
10
INSTR('HelloWorld', 'W')
6
LPAD(salary,10,'*')
*****24000
RPAD(salary, 10, '*')
24000*****
REPLACE
('JACK and JUE','J','BL')
BLACK and BLUE
TRIM('H' FROM 'HelloWorld')
elloWorld
Copyright © 2009, Oracle. All rights reserved.
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Character-Manipulation Functions
CONCAT, SUBSTR, LENGTH, INSTR, LPAD, RPAD, and TRIM are the character-manipulation
functions that are covered in this lesson.
• CONCAT: Joins values together (You are limited to using two parameters with CONCAT.)
• SUBSTR: Extracts a string of determined length
• LENGTH: Shows the length of a string as a numeric value
• INSTR: Finds the numeric position of a named character
• LPAD: Returns an expression left-padded to the length of n characters with a character
expression
• RPAD: Returns an expression right-padded to the length of n characters with a character
expression
• TRIM: Trims leading or trailing characters (or both) from a character string (If
trim_character or trim_source is a character literal, you must enclose it within single
quotation marks.)
Note: You can use functions such as UPPER and LOWER with ampersand substitution. For example,
use UPPER('&job_title')so that the user does not have to enter the job title in a specific case.
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Oracle Database 11g: SQL Fundamentals I 3 - 13
Using the Character-Manipulation Functions
1
SELECT employee_id, CONCAT(first_name, last_name) NAME,
job_id, LENGTH (last_name),
INSTR(last_name, 'a') "Contains 'a'?"
FROM
employees
WHERE SUBSTR(job_id, 4) = 'REP';
1
3
2
Copyright © 2009, Oracle. All rights reserved.
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3
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Using the Character-Manipulation Functions
The slide example displays employee first names and last names joined together, the length of the
employee last name, and the numeric position of the letter “a” in the employee last name for all
employees who have the string, REP, contained in the job ID starting at the fourth position of the
job ID.
Example:
Modify the SQL statement in the slide to display the data for those employees whose last names end
with the letter “n.”
SELECT
LENGTH
FROM
WHERE
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employee_id, CONCAT(first_name, last_name) NAME,
(last_name), INSTR(last_name, 'a') "Contains 'a'?"
employees
SUBSTR(last_name, -1, 1) = 'n';
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Oracle Database 11g: SQL Fundamentals I 3 - 14
Lesson Agenda
•
•
•
•
•
Single-row SQL functions
Character functions
Number functions
Working with dates
Date Functions
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 3 - 15
Number Functions
•
•
•
ROUND: Rounds value to a specified decimal
TRUNC: Truncates value to a specified decimal
MOD: Returns remainder of division
Function
Result
ROUND(45.926, 2)
45.93
TRUNC(45.926, 2)
45.92
MOD(1600, 300)
100
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Number Functions
Number functions accept numeric input and return numeric values. This section describes some of
the number functions.
Function
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Purpose
Rounds the column, expression, or value to n decimal
places or, if n is omitted, no decimal places (If n is
negative, numbers to the left of decimal point are rounded.)
TRUNC(column|expression, n) Truncates the column, expression, or value to n decimal
places or, if n is omitted, n defaults to zero
MOD(m,n)
Returns the remainder of m divided by n
ROUND(column|expression, n)
Note: This list contains only some of the available number functions.
For more information, see the section on Numeric Functions in Oracle Database SQL Language
Reference 11g, Release 1 (11.1).
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Oracle Database 11g: SQL Fundamentals I 3 - 16
Using the ROUND Function
1
2
SELECT ROUND(45.923,2), ROUND(45.923,0),
ROUND(45.923,-1)
FROM
DUAL;
1
2
3
3
DUAL is a dummy table that you can use to view results
from functions and calculations.
Copyright © 2009, Oracle. All rights reserved.
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Using the ROUND Function
The ROUND function rounds the column, expression, or value to n decimal places. If the second
argument is 0 or is missing, the value is rounded to zero decimal places. If the second argument is 2,
the value is rounded to two decimal places. Conversely, if the second argument is –2, the value is
rounded to two decimal places to the left (rounded to the nearest unit of 100).
The ROUND function can also be used with date functions. You will see examples later in this lesson.
DUAL Table
The DUAL table is owned by the user SYS and can be accessed by all users. It contains one column,
DUMMY, and one row with the value X. The DUAL table is useful when you want to return a value
only once (for example, the value of a constant, pseudocolumn, or expression that is not derived from
a table with user data). The DUAL table is generally used for completeness of the SELECT clause
syntax, because both SELECT and FROM clauses are mandatory, and several calculations do not need
to select from the actual tables.
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Oracle Database 11g: SQL Fundamentals I 3 - 17
Using the TRUNC Function
1
2
SELECT TRUNC(45.923,2), TRUNC(45.923),
TRUNC(45.923,-1)
FROM
DUAL;
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Using the TRUNC Function
The TRUNC function truncates the column, expression, or value to n decimal places.
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The TRUNC function works with arguments similar to those of the ROUND function. If the second
argument is 0 or is missing, the value is truncated to zero decimal places. If the second argument is 2,
the value is truncated to two decimal places. Conversely, if the second argument is –2, the value is
truncated to two decimal places to the left. If the second argument is –1, the value is truncated to one
decimal place to the left.
Like the ROUND function, the TRUNC function can be used with date functions.
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Oracle Database 11g: SQL Fundamentals I 3 - 18
Using the MOD Function
For all employees with the job title of Sales Representative,
calculate the remainder of the salary after it is divided by 5,000.
SELECT last_name, salary, MOD(salary, 5000)
FROM
employees
WHERE job_id = 'SA_REP';
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Using the MOD Function
The MOD function finds the remainder of the first argument divided by the second argument. The
slide example calculates the remainder of the salary after dividing it by 5,000 for all employees
whose job ID is SA_REP.
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Note: The MOD function is often used to determine whether a value is odd or even.
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Oracle Database 11g: SQL Fundamentals I 3 - 19
Lesson Agenda
•
•
•
•
•
Single-row SQL functions
Character functions
Number functions
Working with dates
Date functions
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Oracle Database 11g: SQL Fundamentals I 3 - 20
Working with Dates
•
The Oracle database stores dates in an internal numeric
format: century, year, month, day, hours, minutes, and
seconds.
The default date display format is DD-MON-RR.
•
– Enables you to store 21st-century dates in the 20th century
by specifying only the last two digits of the year
– Enables you to store 20th-century dates in the
21st century in the same way
SELECT last_name, hire_date
FROM
employees
WHERE hire_date < '01-FEB-88';
';
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Working with Dates
The Oracle database stores dates in an internal numeric format, representing the century, year,
month, day, hours, minutes, and seconds.
The default display and input format for any date is DD-MON-RR. Valid Oracle dates are between
January 1, 4712 B.C., and December 31, 9999 A.D.
In the example in the slide, the HIRE_DATE column output is displayed in the default format DDMON-RR. However, dates are not stored in the database in this format. All the components of the
date and time are stored. So, although a HIRE_DATE such as 17-JUN-87 is displayed as day, month,
and year, there is also time and century information associated with the date. The complete data
might be June 17, 1987, 5:10:43 PM.
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Oracle Database 11g: SQL Fundamentals I 3 - 21
RR Date Format
Current Year
1995
1995
2001
2001
Specified Date
27-OCT-95
27-OCT-17
27-OCT-17
27-OCT-95
YY Format
RR Format
1995
2017
2017
1995
1995
1917
2017
2095
If the specified two-digit year is:
If two digits
of the
current
year are:
0–49
50–99
0–49
The return date is in
the current century
50–99
The return date is in
the century after
the current one
The return date is in
the century before
the current one
The return date is in
the current century
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Copyright © 2009, Oracle. All rights reserved.
RR Date Format
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The RR date format is similar to the YY element, but you can use it to specify different centuries. Use
the RR date format element instead of YY so that the century of the return value varies according to
the specified two-digit year and the last two digits of the current year. The table in the slide
summarizes the behavior of the RR element.
Current Year
1994
1994
2001
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Given Date
Interpreted (RR)
Interpreted (YY)
27-OCT-95
1995
1995
27-OCT-17
2017
1917
27-OCT-17
2017
2017
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Oracle Database 11g: SQL Fundamentals I 3 - 22
RR Date Format (continued)
This data is stored internally as follows:
CENTURY YEAR MONTH
DAY
HOUR MINUTE
SECOND
19
87
06
17
17
10
43
Centuries and the Year 2000
When a record with a date column is inserted into a table, the century information is picked up from
the SYSDATE function. However, when the date column is displayed on the screen, the century
component is not displayed (by default).
The DATE data type uses 2 bytes for the year information, one for century and one for year. The
century value is always included, whether or not it is specified or displayed. In this case, RR
determines the default value for century on INSERT.
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Oracle Database 11g: SQL Fundamentals I 3 - 23
Using the SYSDATE Function
SYSDATE is a function that returns:
•
•
Date
Time
SELECT sysdate
FROM
dual;
;
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Copyright © 2009, Oracle. All rights reserved.
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Using the SYSDATE Function
SYSDATE is a date function that returns the current database server date and time. You can use
SYSDATE just as you would use any other column name. For example, you can display the current
date by selecting SYSDATE from a table. It is customary to select SYSDATE from a dummy table
called DUAL.
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Note: SYSDATE returns the current date and time set for the operating system on which the database
resides. Therefore, if you are in a place in Australia and connected to a remote database in a location
in the United States (US), sysdate function will return the US date and time. In that case, you can
use the CURRENT_DATE function that returns the current date in the session time zone.
The CURRENT_DATE function and other related time zone functions are discussed in detail in the
course titled Oracle Database 11g: SQL Fundamentals II.
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Oracle Database 11g: SQL Fundamentals I 3 - 24
Arithmetic with Dates
•
•
Add or subtract a number to or from a date for a resultant
date value.
Subtract two dates to find the number of days between
those dates.
Add hours to a date by dividing the number of hours by 24.
•
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Arithmetic with Dates
Because the database stores dates as numbers, you can perform calculations using arithmetic
operators such as addition and subtraction. You can add and subtract number constants as well as
dates.
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You can perform the following operations:
Operation
date + number
date – number
date – date
date + number/24
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Result
Description
Date
Date
Adds a number of days to a date
Subtracts a number of days from a date
Number of days
Date
Subtracts one date from another
Adds a number of hours to a date
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Oracle Database 11g: SQL Fundamentals I 3 - 25
Using Arithmetic Operators
with Dates
SELECT last_name, (SYSDATE-hire_date)/7 AS WEEKS
FROM
employees
WHERE department_id = 90;
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Using Arithmetic Operators with Dates
The example in the slide displays the last name and the number of weeks employed for all employees
in department 90. It subtracts the date on which the employee was hired from the current date
(SYSDATE) and divides the result by 7 to calculate the number of weeks that a worker has been
employed.
Note: SYSDATE is a SQL function that returns the current date and time. Your results may differ
depending on the date and time set for the operating system of your local database when you run the
SQL query.
If a more current date is subtracted from an older date, the difference is a negative number.
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Oracle Database 11g: SQL Fundamentals I 3 - 26
Lesson Agenda
•
•
•
•
•
Single-row SQL functions
Character functions
Number functions
Working with dates
Date functions
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 3 - 27
Date-Manipulation Functions
Function
Result
MONTHS_BETWEEN
Number of months between two dates
ADD_MONTHS
Add calendar months to date
NEXT_DAY
Next day of the date specified
LAST_DAY
Last day of the month
ROUND
Round date
TRUNC
Truncate date
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Date-Manipulation Functions
Date functions operate on Oracle dates. All date functions return a value of the DATE data type
except MONTHS_BETWEEN, which returns a numeric value.
• MONTHS_BETWEEN(date1, date2): Finds the number of months between date1 and
date2. The result can be positive or negative. If date1 is later than date2, the result is
positive; if date1 is earlier than date2, the result is negative. The noninteger part of the result
represents a portion of the month.
• ADD_MONTHS(date, n): Adds n number of calendar months to date. The value of n must
be an integer and can be negative.
• NEXT_DAY(date, 'char'): Finds the date of the next specified day of the week
('char') following date. The value of char may be a number representing a day or a
character string.
• LAST_DAY(date): Finds the date of the last day of the month that contains date
The above list is a subset of the available date functions. ROUND and TRUNC number functions can
also be used to manipulate the date values as shown below:
• ROUND(date[,'fmt']): Returns date rounded to the unit that is specified by the format
model fmt. If the format model fmt is omitted, date is rounded to the nearest day.
• TRUNC(date[, 'fmt']): Returns date with the time portion of the day truncated to the
unit that is specified by the format model fmt. If the format model fmt is omitted, date is
truncated to the nearest day.
The format models are covered in detail in the next lesson titled “Using Conversion Functions and
Conditional Expressions.”
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Oracle Database 11g: SQL Fundamentals I 3 - 28
Using Date Functions
Function
Result
MONTHS_BETWEEN
('01-SEP-95','11-JAN-94')
19.6774194
ADD_MONTHS (‘31-JAN-96',1)
‘29-FEB-96'
NEXT_DAY
('01-SEP-95','FRIDAY')
'08-SEP-95'
LAST_DAY
('01-FEB-95')
'28-FEB-95'
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Copyright © 2009, Oracle. All rights reserved.
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Using Date Functions
In the slide example, the ADD_MONTHS function adds one month to the supplied date value, “31JAN-96” and returns “29-FEB-96.” The function recognizes the year 1996 as the leap year and hence
returns the last day of the February month. If you change the input date value to “31-JAN-95,” the
function returns “28-FEB-95.”
For example, display the employee number, hire date, number of months employed, six-month
review date, first Friday after hire date, and the last day of the hire month for all employees who have
been employed for fewer than 100 months.
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SELECT employee_id, hire_date,
MONTHS_BETWEEN (SYSDATE, hire_date) TENURE,
ADD_MONTHS (hire_date, 6) REVIEW,
NEXT_DAY (hire_date, 'FRIDAY'), LAST_DAY(hire_date)
FROM
employees
WHERE MONTHS_BETWEEN (SYSDATE, hire_date) < 100;
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Oracle Database 11g: SQL Fundamentals I 3 - 29
Using ROUND and TRUNC Functions with Dates
Assume SYSDATE = '25-JUL-03':
Function
Result
ROUND(SYSDATE,'MONTH')
01-AUG-03
ROUND(SYSDATE ,'YEAR')
01-JAN-04
TRUNC(SYSDATE ,'MONTH')
01-JUL-03
TRUNC(SYSDATE ,'YEAR')
01-JAN-03
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Copyright © 2009, Oracle. All rights reserved.
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Using ROUND and TRUNC Functions with Dates
The ROUND and TRUNC functions can be used for number and date values. When used with dates,
these functions round or truncate to the specified format model. Therefore, you can round dates to the
nearest year or month. If the format model is month, dates 1-15 result in the first day of the current
month. Dates 16-31 result in the first day of the next month. If the format model is year, months 1-6
result in January 1 of the current year. Months 7-12 result in January 1 of the next year.
Example:
Compare the hire dates for all employees who started in 1997. Display the employee number, hire
date, and starting month using the ROUND and TRUNC functions.
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SELECT employee_id, hire_date,
ROUND(hire_date, 'MONTH'), TRUNC(hire_date, 'MONTH')
FROM
employees
WHERE hire_date LIKE '%97';
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Oracle Database 11g: SQL Fundamentals I 3 - 30
Quiz
Which of the following statements are true about single-row
functions?
1. Manipulate data items
2. Accept arguments and return one value per argument
3. Act on each row that is returned
4. Return one result per set of rows
5. May not modify the data type
6. Can be nested
7. Accept arguments that can be a column or an expression
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Copyright © 2009, Oracle. All rights reserved.
Answer: 1, 3, 6, 7
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Oracle Database 11g: SQL Fundamentals I 3 - 31
Summary
In this lesson, you should have learned how to:
• Perform calculations on data using functions
• Modify individual data items using functions
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Summary
Single-row functions can be nested to any level. Single-row functions can manipulate the following:
• Character data: LOWER, UPPER, INITCAP, CONCAT, SUBSTR, INSTR, LENGTH
• Number data: ROUND, TRUNC, MOD
• Date values: SYSDATE, MONTHS_BETWEEN, ADD_MONTHS, NEXT_DAY, LAST_DAY
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Remember the following:
• Date values can also use arithmetic operators.
• ROUND and TRUNC functions can also be used with date values.
SYSDATE and DUAL
SYSDATE is a date function that returns the current date and time. It is customary to select
SYSDATE from a dummy table called DUAL.
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Oracle Database 11g: SQL Fundamentals I 3 - 32
Practice 3: Overview
This practice covers the following topics:
• Writing a query that displays the current date
• Creating queries that require the use of numeric,
character, and date functions
• Performing calculations of years and months of service for
an employee
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Copyright © 2009, Oracle. All rights reserved.
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Practice 3: Overview
This practice provides a variety of exercises using different functions that are available for character,
number, and date data types.
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Oracle Database 11g: SQL Fundamentals I 3 - 33
Practice 3
Part 1
1. Write a query to display the system date. Label the column as Date.
Note: If your database is remotely located in a different time zone, the output will be the date
for the operating system on which the database resides.
2. The HR department needs a report to display the employee number, last name, salary, and
salary increased by 15.5% (expressed as a whole number) for each employee. Label the column
New Salary. Save your SQL statement in a file named lab_03_02.sql.
3. Run your query in the lab_03_02.sql file.
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4. Modify your query lab_03_02.sql to add a column that subtracts the old salary from the
new salary. Label the column Increase. Save the contents of the file as lab_03_04.sql.
Run the revised query.
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…
Oracle Database 11g: SQL Fundamentals I 3 - 34
Practice 3 (continued)
5. Write a query that displays the last name (with the first letter in uppercase and all the other
letters in lowercase) and the length of the last name for all employees whose name starts with
the letters “J,” “A,” or “M.” Give each column an appropriate label. Sort the results by the
employees’ last names.
Rewrite the query so that the user is prompted to enter a letter that the last name starts with. For
example, if the user enters “H” (capitalized) when prompted for a letter, then the output should
show all employees whose last name starts with the letter “H.”
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Modify the query such that the case of the entered letter does not affect the output. The entered
letter must be capitalized before being processed by the SELECT query.
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Oracle Database 11g: SQL Fundamentals I 3 - 35
Practice 3 (continued)
6. The HR department wants to find the duration of employment for each employee. For each
employee, display the last name and calculate the number of months between today and the
date on which the employee was hired. Label the column as MONTHS_WORKED. Order your
results by the number of months employed. Round the number of months up to the closest
whole number.
Note: Because this query depends on the date when it was executed, the values in the
MONTHS_WORKED column will differ for you.
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Oracle Database 11g: SQL Fundamentals I 3 - 36
Practice 3 (continued)
If you have time, complete the following exercises:
7. Create a query to display the last name and salary for all employees. Format the salary to be 15
characters long, left-padded with the $ symbol. Label the column as SALARY.
…
8. Create a query that displays the first eight characters of the employees’ last names and indicates
the amounts of their salaries with asterisks. Each asterisk signifies a thousand dollars. Sort the
data in descending order of salary. Label the column as
EMPLOYEES_AND_THEIR_SALARIES.
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9. Create a query to display the last name and the number of weeks employed for all employees in
department 90. Label the number of weeks column as TENURE. Truncate the number of weeks
value to 0 decimal places. Show the records in descending order of the employee’s tenure.
Note: The TENURE value will differ as it depends on the date on which you run the query.
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Oracle Database 11g: SQL Fundamentals I 3 - 37
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Using Conversion Functions and
Conditional Expressions
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Copyright © 2009, Oracle. All rights reserved.
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Objectives
After completing this lesson, you should be able to do the
following:
• Describe various types of conversion functions that are
available in SQL
• Use the TO_CHAR, TO_NUMBER, and TO_DATE conversion
functions
•
Apply conditional expressions in a SELECT statement
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Copyright © 2009, Oracle. All rights reserved.
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Objectives
This lesson focuses on functions that convert data from one type to another (for example, conversion
from character data to numeric data) and discusses the conditional expressions in SQL SELECT
statements.
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Oracle Database 11g: SQL Fundamentals I 4 - 2
Lesson Agenda
•
•
Implicit and explicit data type conversion
TO_CHAR, TO_DATE, TO_NUMBER functions
•
•
Nesting functions
General functions:
–
–
–
–
•
NVL
NVL2
NULLIF
COALESCE
Conditional expressions:
– CASE
– DECODE
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 4 - 3
Conversion Functions
Data type
conversion
Implicit data type
conversion
Explicit data type
conversion
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Copyright © 2009, Oracle. All rights reserved.
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Conversion Functions
In addition to Oracle data types, columns of tables in an Oracle database can be defined by using the
American National Standards Institute (ANSI), DB2, and SQL/DS data types. However, the Oracle
server internally converts such data types to Oracle data types.
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In some cases, the Oracle server receives data of one data type where it expects data of a different
data type. When this happens, the Oracle server can automatically convert the data to the expected
data type. This data type conversion can be done implicitly by the Oracle server or explicitly by the
user.
Implicit data type conversions work according to the rules explained in the next two slides.
Explicit data type conversions are done by using the conversion functions. Conversion functions
convert a value from one data type to another. Generally, the form of the function names follows the
convention data type TO data type. The first data type is the input data type and the second
data type is the output.
Note: Although implicit data type conversion is available, it is recommended that you do the explicit
data type conversion to ensure the reliability of your SQL statements.
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Oracle Database 11g: SQL Fundamentals I 4 - 4
Implicit Data Type Conversion
In expressions, the Oracle server can automatically convert the
following:
From
To
VARCHAR2 or CHAR
NUMBER
VARCHAR2 or CHAR
DATE
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Implicit Data Type Conversion
Oracle server can automatically perform data type conversion in an expression. For example, the
expression hire_date > '01-JAN-90' results in the implicit conversion from the string '01JAN-90' to a date. Therefore, a VARCHAR2 or CHAR value can be implicitly converted to a number
or date data type in an expression.
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Oracle Database 11g: SQL Fundamentals I 4 - 5
Implicit Data Type Conversion
For expression evaluation, the Oracle server can automatically
convert the following:
From
To
NUMBER
VARCHAR2 or CHAR
DATE
VARCHAR2 or CHAR
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Copyright © 2009, Oracle. All rights reserved.
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Implicit Data Type Conversion (continued)
In general, the Oracle server uses the rule for expressions when a data type conversion is needed. For
example, the expression grade = 2 results in the implicit conversion of the number 20000 to the
string “2” because grade is a CHAR(2) column.
Note: CHAR to NUMBER conversions succeed only if the character string represents a valid number.
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Oracle Database 11g: SQL Fundamentals I 4 - 6
Explicit Data Type Conversion
TO_NUMBER
NUMBER
TO_DATE
CHARACTER
TO_CHAR
DATE
TO_CHAR
Copyright © 2009, Oracle. All rights reserved.
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Explicit Data Type Conversion
SQL provides three functions to convert a value from one data type to another:
Function
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Purpose
TO_CHAR(number|date,[ fmt], Converts a number or date value to a VARCHAR2
[nlsparams])
character string with the format model fmt
Number conversion: The nlsparams
parameter specifies the following characters,
which are returned by number format elements:
•
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Decimal character
Group separator
Local currency symbol
International currency symbol
If nlsparams or any other parameter is omitted,
this function uses the default parameter values for
the session.
Oracle Database 11g: SQL Fundamentals I 4 - 7
Explicit Data Type Conversion
TO_NUMBER
TO_DATE
CHARACTER
NUMBER
TO_CHAR
TO_CHAR
Copyright © 2009, Oracle. All rights reserved.
Explicit Data Type Conversion (continued)
Function
DATE
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Purpose
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TO_CHAR(number|date,[ fmt],
[nlsparams])
Date conversion: The nlsparams parameter specifies
the language in which the month and day names, and
abbreviations are returned. If this parameter is omitted,
this function uses the default date languages for the
session.
TO_NUMBER(char,[fmt],
[nlsparams])
Converts a character string containing digits to a number
in the format specified by the optional format model fmt.
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The nlsparams parameter has the same purpose in this
function as in the TO_CHAR function for number
conversion.
TO_DATE(char,[fmt],[nlspara
ms])
Converts a character string representing a date to a date
value according to the fmt that is specified. If fmt is
omitted, the format is DD-MON-YY.
The nlsparams parameter has the same purpose in this
function as in the TO_CHAR function for date conversion.
Oracle Database 11g: SQL Fundamentals I 4 - 8
Explicit Data Type Conversion (continued)
Note: The list of functions mentioned in this lesson includes only some of the available conversion
functions.
For more information, see the section on Conversion Functions in Oracle Database SQL Language
Reference 11g, Release 1 (11.1).
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Oracle Database 11g: SQL Fundamentals I 4 - 9
Lesson Agenda
•
•
Implicit and explicit data type conversion
TO_CHAR, TO_DATE, TO_NUMBER functions
•
•
Nesting functions
General functions:
–
–
–
–
•
NVL
NVL2
NULLIF
COALESCE
Conditional expressions:
– CASE
– DECODE
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Oracle Database 11g: SQL Fundamentals I 4 - 10
Using the TO_CHAR Function with Dates
TO_CHAR(date, 'format_model')
The format model:
• Must be enclosed with single quotation marks
• Is case-sensitive
• Can include any valid date format element
• Has an fm element to remove padded blanks or suppress
leading zeros
• Is separated from the date value by a comma
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Using the TO_CHAR Function with Dates
TO_CHAR converts a datetime data type to a value of VARCHAR2 data type in the format specified
by the format_model. A format model is a character literal that describes the format of datetime
stored in a character string. For example, the datetime format model for the string '11-Nov1999' is 'DD-Mon-YYYY'. You can use the TO_CHAR function to convert a date from its default
format to the one that you specify.
Guidelines
• The format model must be enclosed with single quotation marks and is case-sensitive.
• The format model can include any valid date format element. But be sure to separate the date
value from the format model with a comma.
• The names of days and months in the output are automatically padded with blanks.
• To remove padded blanks or to suppress leading zeros, use the fill mode fm element.
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SELECT employee_id, TO_CHAR(hire_date, 'MM/YY') Month_Hired
FROM
employees
WHERE last_name = 'Higgins';
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Oracle Database 11g: SQL Fundamentals I 4 - 11
Elements of the Date Format Model
Element
Result
YYYY
Full year in numbers
YEAR
Year spelled out (in English)
MM
Two-digit value for the month
MONTH
Full name of the month
MON
Three-letter abbreviation of the month
DY
Three-letter abbreviation of the day of the week
DAY
Full name of the day of the week
DD
Numeric day of the month
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Oracle Database 11g: SQL Fundamentals I 4 - 12
Sample Format Elements of Valid Date Formats
Element
Description
SCC or CC
Century; server prefixes B.C. date with -
Years in dates YYYY or SYYYY Year; server prefixes B.C. date with YYY or YY or Y
Last three, two, or one digit of the year
Y,YYY
Year with comma in this position
IYYY, IYY, IY, I
Four-, three-, two-, or one-digit year based on the ISO
standard
SYEAR or YEAR
Year spelled out; server prefixes B.C. date with -
BC or AD
Indicates B.C. or A.D. year
B.C. or A.D.
Indicates B.C. or A.D. year using periods
Q
Quarter of year
MM
Month: two-digit value
MONTH
Name of the month padded with blanks to a length of nine
characters
MON
Name of the month, three-letter abbreviation
RM
Roman numeral month
WW or W
Week of the year or month
DDD or DD or D
Day of the year, month, or week
DAY
Name of the day padded with blanks to a length of nine
characters
DY
Name of the day; three-letter abbreviation
J
Julian day; the number of days since December 31, 4713
B.C.
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Weeks in the year from ISO standard (1 to 53)
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Oracle Database 11g: SQL Fundamentals I 4 - 13
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•
Time elements format the time portion of the date:
HH24:MI:SS AM
•
15:45:32 PM
Add character strings by enclosing them with double
quotation marks:
DD "of" MONTH
•
12 of OCTOBER
Number suffixes spell out numbers:
ddspth
fourteenth
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Elements of the Date Format Model
Use the formats that are listed in the following tables to display time information and literals, and to
change numerals to spelled numbers.
Element
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Description
AM or PM
A.M. or P.M.
HH or HH12 or HH24
MI
SS
SSSSS
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Meridian indicator
Meridian indicator with periods
Hour of day, or hour (1–12), or hour (0–23)
Minute (0–59)
Second (0–59)
Seconds past midnight (0–86399)
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Oracle Database 11g: SQL Fundamentals I 4 - 14
Other Formats
Element
Description
/ . ,
Punctuation is reproduced in the result.
“of the”
Quoted string is reproduced in the result.
Specifying Suffixes to Influence Number Display
Element
Description
TH
Ordinal number (for example, DDTH for 4TH)
SP
Spelled-out number (for example, DDSP for FOUR)
SPTH or THSP
Spelled-out ordinal numbers (for example, DDSPTH for
FOURTH)
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Oracle Database 11g: SQL Fundamentals I 4 - 15
Using the TO_CHAR Function with Dates
SELECT last_name,
TO_CHAR(hire_date, 'fmDD Month YYYY')
AS HIREDATE
FROM
employees;
…
Copyright © 2009, Oracle. All rights reserved.
Using the TO_CHAR Function with Dates
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The SQL statement in the slide displays the last names and hire dates for all the employees. The hire
date appears as 17 June 1987.
Example:
Modify the example in the slide to display the dates in a format that appears as “Seventeenth of June
1987 12:00:00 AM.”
SELECT last_name,
TO_CHAR(hire_date,
'fmDdspth "of" Month YYYY fmHH:MI:SS AM')
HIREDATE
FROM
employees;
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Notice that the month follows the format model specified; in other words, the first letter is capitalized
and the rest are in lowercase.
Oracle Database 11g: SQL Fundamentals I 4 - 16
Using the TO_CHAR Function with Numbers
TO_CHAR(number, 'format_model')
These are some of the format elements that you can use with
the TO_CHAR function to display a number value as a
character:
Element
9
Result
0
Forces a zero to be displayed
$
Places a floating dollar sign
L
Uses the floating local currency symbol
.
Prints a decimal point
,
Prints a comma as a thousands indicator
Represents a number
Copyright © 2009, Oracle. All rights reserved.
Using the TO_CHAR Function with Numbers
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When working with number values, such as character strings, you should convert those numbers to
the character data type using the TO_CHAR function, which translates a value of NUMBER data type
to VARCHAR2 data type. This technique is especially useful with concatenation.
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Oracle Database 11g: SQL Fundamentals I 4 - 17
Using the TO_CHAR Function with Numbers (continued)
Number Format Elements
If you are converting a number to the character data type, you can use the following format elements:
Element
Description
Example
Result
9
Numeric position (number of 9s determine display
width)
999999
1234
0
Display leading zeros
099999
001234
$
Floating dollar sign
$999999
$1234
L
Floating local currency symbol
L999999
FF1234
D
Returns the decimal character in the specified
position. The default is a period (.).
99D99
99.99
.
Decimal point in position specified
999999.99
1234.00
G
Returns the group separator in the specified
position. You can specify multiple group
separators in a number format model.
9,999
9G999
,
Comma in position specified
999,999
1,234
MI
Minus signs to right (negative values)
999999MI
1234-
PR
Parenthesize negative numbers
999999PR
<1234>
EEEE
Scientific notation (format must specify four Es)
99.999EEEE
U
Returns in the specified position the “Euro” (or
other) dual currency
U9999
V
Multiply by 10 n times (n = number of 9s after V)
9999V99
123400
S
Returns the negative or positive value
S9999
-1234 or
+1234
B
Display zero values as blank, not 0
B9999.99
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Oracle Database 11g: SQL Fundamentals I 4 - 18
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1.234E+03
€1234
1234.00
Using the TO_CHAR Function with Numbers
SELECT TO_CHAR(salary, '$99,999.00') SALARY
FROM
employees
WHERE last_name = 'Ernst';
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Using the TO_CHAR Function with Numbers (continued)
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• The Oracle server displays a string of number signs (#) in place of a whole number whose digits
exceed the number of digits provided in the format model.
• The Oracle server rounds the stored decimal value to the number of decimal places provided in
the format model.
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Oracle Database 11g: SQL Fundamentals I 4 - 19
Using the TO_NUMBER and TO_DATE Functions
•
Convert a character string to a number format using the
TO_NUMBER function:
TO_NUMBER(char[, 'format_model'])
•
Convert a character string to a date format using the
TO_DATE function:
TO_DATE(char[, 'format_model'])
•
These functions have an fx modifier. This modifier
specifies the exact match for the character argument and
date format model of a TO_DATE function.
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Using the TO_NUMBER and TO_DATE Functions
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You may want to convert a character string to either a number or a date. To accomplish this task, use
the TO_NUMBER or TO_DATE functions. The format model that you select is based on the
previously demonstrated format elements.
The fx modifier specifies the exact match for the character argument and date format model of a
TO_DATE function:
• Punctuation and quoted text in the character argument must exactly match (except for case) the
corresponding parts of the format model.
• The character argument cannot have extra blanks. Without fx, the Oracle server ignores extra
blanks.
• Numeric data in the character argument must have the same number of digits as the
corresponding element in the format model. Without fx, the numbers in the character argument
can omit leading zeros.
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Oracle Database 11g: SQL Fundamentals I 4 - 20
Using the TO_NUMBER and TO_DATE Functions (continued)
Example:
Display the name and hire date for all employees who started on May 24, 1999. There are two spaces
after the month May and before the number 24 in the following example. Because the fx modifier is
used, an exact match is required and the spaces after the word May are not recognized:
SELECT last_name, hire_date
FROM
employees
WHERE hire_date = TO_DATE('May
24, 1999', 'fxMonth DD, YYYY');
The resulting error output looks like this:
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Oracle Database 11g: SQL Fundamentals I 4 - 21
Using the TO_CHAR and TO_DATE Function
with RR Date Format
To find employees hired before 1990, use the RR date format,
which produces the same results whether the command is run
in 1999 or now:
SELECT last_name, TO_CHAR(hire_date, 'DD-Mon-YYYY')
FROM employees
WHERE hire_date < TO_DATE('01-Jan-90','DD-Mon-RR');
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Using the TO_CHAR and TO_DATE Function with RR Date Format
To find employees who were hired before 1990, the RR format can be used. Because the current year
is greater than 1999, the RR format interprets the year portion of the date from 1950 to 1999.
The following command, on the other hand, results in no rows being selected because the YY format
interprets the year portion of the date in the current century (2090).
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SELECT last_name, TO_CHAR(hire_date, 'DD-Mon-yyyy')
FROM
employees
WHERE TO_DATE(hire_date, 'DD-Mon-yy') < '01-Jan-1990';
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Oracle Database 11g: SQL Fundamentals I 4 - 22
Lesson Agenda
•
•
Implicit and explicit data type conversion
TO_CHAR, TO_DATE, TO_NUMBER functions
•
•
Nesting functions
General functions:
–
–
–
–
•
NVL
NVL2
NULLIF
COALESCE
Conditional expressions:
– CASE
– DECODE
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Oracle Database 11g: SQL Fundamentals I 4 - 23
Nesting Functions
•
•
Single-row functions can be nested to any level.
Nested functions are evaluated from the deepest level to
the least deep level.
F3(F2(F1(col,arg1),arg2),arg3)
Step 1 = Result 1
Step 2 = Result 2
Step 3 = Result 3
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Nesting Functions
Single-row functions can be nested to any depth. Nested functions are evaluated from the innermost
level to the outermost level. Some examples follow to show you the flexibility of these functions.
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Oracle Database 11g: SQL Fundamentals I 4 - 24
Nesting Functions
SELECT last_name,
UPPER(CONCAT(SUBSTR (LAST_NAME, 1, 8), '_US'))
FROM
employees
WHERE department_id = 60;
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Nesting Functions (continued)
The slide example displays the last names of employees in department 60. The evaluation of the SQL
statement involves three steps:
1. The inner function retrieves the first eight characters of the last name.
Result1 = SUBSTR (LAST_NAME, 1, 8)
2. The outer function concatenates the result with _US.
Result2 = CONCAT(Result1, '_US')
3. The outermost function converts the results to uppercase.
The entire expression becomes the column heading because no column alias was given.
Example:
Display the date of the next Friday that is six months from the hire date. The resulting date should
appear as Friday, August 13th, 1999. Order the results by hire date.
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SELECT
TO_CHAR(NEXT_DAY(ADD_MONTHS
(hire_date, 6), 'FRIDAY'),
'fmDay, Month ddth, YYYY')
"Next 6 Month Review"
FROM
employees
ORDER BY hire_date;
Oracle Database 11g: SQL Fundamentals I 4 - 25
Lesson Agenda
•
•
Implicit and explicit data type conversion
TO_CHAR, TO_DATE, TO_NUMBER functions
•
•
Nesting functions
General functions:
–
–
–
–
•
NVL
NVL2
NULLIF
COALESCE
Conditional expressions:
– CASE
– DECODE
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Oracle Database 11g: SQL Fundamentals I 4 - 26
General Functions
The following functions work with any data type and pertain to
using nulls:
• NVL (expr1, expr2)
• NVL2 (expr1, expr2, expr3)
• NULLIF (expr1, expr2)
• COALESCE (expr1, expr2, ..., exprn)
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General Functions
These functions work with any data type and pertain to the use of null values in the expression list.
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Function
Description
NVL
Converts a null value to an actual value
NVL2
If expr1 is not null, NVL2 returns expr2. If expr1 is null, NVL2
returns expr3. The argum ent expr1 can have any data type.
NULLIF
Com pares two expressions and returns null if they are equal; returns
the first expression if they are not equal
COALESCE
Returns the first non-null expression in the expression list
Note: For more information about the hundreds of functions available, see the section on Functions
in Oracle Database SQL Language Reference 11g, Release 1 (11.1).
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Oracle Database 11g: SQL Fundamentals I 4 - 27
NVL Function
Converts a null value to an actual value:
• Data types that can be used are date, character, and
number.
• Data types must match:
– NVL(commission_pct,0)
– NVL(hire_date,'01-JAN-97')
– NVL(job_id,'No Job Yet')
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NVL Function
To convert a null value to an actual value, use the NVL function.
Syntax
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NVL (expr1, expr2)
In the syntax:
• expr1 is the source value or expression that may contain a null
• expr2 is the target value for converting the null
You can use the NVL function to convert any data type, but the return value is always the same as the
data type of expr1.
NVL Conversions for Various Data Types
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Data Type
NUMBER
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DATE
Conversion Example
NVL(number_column,9)
NVL(date_column, '01-JAN-95')
CHAR or VARCHAR2
NVL(character_column, 'Unavailable')
Oracle Database 11g: SQL Fundamentals I 4 - 28
Using the NVL Function
1
SELECT last_name, salary, NVL(commission_pct, 0),
(salary*12) + (salary*12*NVL(commission_pct, 0)) AN_SAL
FROM employees;
…
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Copyright © 2009, Oracle. All rights reserved.
Using the NVL Function
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To calculate the annual compensation of all employees, you need to multiply the monthly salary by
12 and then add the commission percentage to the result:
SELECT last_name, salary, commission_pct,
(salary*12) + (salary*12*commission_pct) AN_SAL
FROM
employees;
…
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Notice that the annual compensation is calculated for only those employees who earn a commission.
If any column value in an expression is null, the result is null. To calculate values for all employees,
you must convert the null value to a number before applying the arithmetic operator. In the example
in the slide, the NVL function is used to convert null values to zero.
Oracle Database 11g: SQL Fundamentals I 4 - 29
Using the NVL2 Function
SELECT last_name, salary, commission_pct,
1
NVL2(commission_pct,
2
'SAL+COMM', 'SAL') income
FROM
employees WHERE department_id IN (50, 80);
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Using the NVL2 Function
The NVL2 function examines the first expression. If the first expression is not null, then the NVL2
function returns the second expression. If the first expression is null, then the third expression is
returned.
Syntax
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NVL2(expr1, expr2, expr3)
In the syntax:
• expr1 is the source value or expression that may contain a null
• expr2 is the value that is returned if expr1 is not null
• expr3 is the value that is returned if expr1 is null
In the example shown in the slide, the COMMISSION_PCT column is examined. If a value is
detected, the text literal value of SAL+COMM is returned. If the COMMISSION_PCT column contains
a null value, the text literal value of SAL is returned.
Notes: The argument expr1 can have any data type. The arguments expr2 and expr3 can have
any data types except LONG.
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Oracle Database 11g: SQL Fundamentals I 4 - 30
Using the NULLIF Function
1
SELECT first_name, LENGTH(first_name) "expr1",
2
last_name, LENGTH(last_name) "expr2",
NULLIF(LENGTH(first_name), LENGTH(last_name)) result
FROM
employees;
3
…
1
2
Copyright © 2009, Oracle. All rights reserved.
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Using the NULLIF Function
The NULLIF function compares two expressions. If they are equal, the function returns a null. If
they are not equal, the function returns the first expression. However, you cannot specify the literal
NULL for the first expression.
Syntax
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NULLIF (expr1, expr2)
In the syntax:
• NULLIF compares expr1 and expr2. If they are equal, then the function returns null. If they
are not, then the function returns expr1. However, you cannot specify the literal NULL for
expr1.
In the example shown in the slide, the length of the first name in the EMPLOYEES table is compared
to the length of the last name in the EMPLOYEES table. When the lengths of the names are equal, a
null value is displayed. When the lengths of the names are not equal, the length of the first name is
displayed.
Note: The NULLIF function is logically equivalent to the following CASE expression. The CASE
expression is discussed on a subsequent page:
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CASE WHEN expr1 = expr 2 THEN NULL ELSE expr1 END
Oracle Database 11g: SQL Fundamentals I 4 - 31
Using the COALESCE Function
•
•
The advantage of the COALESCE function over the NVL
function is that the COALESCE function can take multiple
alternate values.
If the first expression is not null, the COALESCE function
returns that expression; otherwise, it does a COALESCE of
the remaining expressions.
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Using the COALESCE Function
The COALESCE function returns the first non-null expression in the list.
Syntax
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COALESCE (expr1, expr2, ... exprn)
In the syntax:
• expr1 returns this expression if it is not null
• expr2 returns this expression if the first expression is null and this expression is not null
• exprn returns this expression if the preceding expressions are null
Note that all expressions must be of the same data type.
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Oracle Database 11g: SQL Fundamentals I 4 - 32
Using the COALESCE Function
SELECT last_name, employee_id,
COALESCE(TO_CHAR(commission_pct),TO_CHAR(manager_id),
'No commission and no manager')
FROM employees;
…
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Using the COALESCE Function (continued)
In the example shown in the slide, if the manager_id value is not null, it is displayed. If the
manager_id value is null, then the commission_pct is displayed. If the manager_id and
commission_pct values are null, then “No commission and no manager” is displayed. Note,
TO_CHAR function is applied so that all expressions are of the same data type.
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Oracle Database 11g: SQL Fundamentals I 4 - 33
Using the COALESCE Function (continued)
Example:
For the employees who do not get any commission, your organization wants to give a salary
increment of $2,000 and for employees who get commission, the query should compute the new
salary that is equal to the existing salary added to the commission amount.
SELECT last_name, salary, commission_pct,
COALESCE((salary+(commission_pct*salary)), salary+2000, salary) "New
Salary"
FROM
employees;
Note: Examine the output. For employees who do not get any commission, the New Salary column
shows the salary incremented by $2,000 and for employees who get commission, the New Salary
column shows the computed commission amount added to the salary.
…
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Oracle Database 11g: SQL Fundamentals I 4 - 34
Lesson Agenda
•
•
Implicit and explicit data type conversion
TO_CHAR, TO_DATE, TO_NUMBER functions
•
•
Nesting functions
General functions:
–
–
–
–
•
NVL
NVL2
NULLIF
COALESCE
Conditional expressions:
– CASE
– DECODE
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Oracle Database 11g: SQL Fundamentals I 4 - 35
Conditional Expressions
•
•
Provide the use of the IF-THEN-ELSE logic within a SQL
statement
Use two methods:
– CASE expression
– DECODE function
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Conditional Expressions
The two methods that are used to implement conditional processing (IF-THEN-ELSE logic) in a
SQL statement are the CASE expression and the DECODE function.
Note: The CASE expression complies with the ANSI SQL. The DECODE function is specific to
Oracle syntax.
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Oracle Database 11g: SQL Fundamentals I 4 - 36
CASE Expression
Facilitates conditional inquiries by doing the work of an
IF-THEN-ELSE statement:
CASE expr WHEN
[WHEN
WHEN
ELSE
END
comparison_expr1 THEN return_expr1
comparison_expr2 THEN return_expr2
comparison_exprn THEN return_exprn
else_expr]
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CASE Expression
CASE expressions allow you to use the IF-THEN-ELSE logic in SQL statements without having to
invoke procedures.
In a simple CASE expression, the Oracle server searches for the first WHEN ... THEN pair for
which expr is equal to comparison_expr and returns return_expr. If none of the WHEN
... THEN pairs meet this condition, and if an ELSE clause exists, then the Oracle server returns
else_expr. Otherwise, the Oracle server returns a null. You cannot specify the literal NULL for all
the return_exprs and the else_expr.
All of the expressions ( expr, comparison_expr, and return_expr) must be of the same
data type, which can be CHAR, VARCHAR2, NCHAR, or NVARCHAR2.
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Oracle Database 11g: SQL Fundamentals I 4 - 37
Using the CASE Expression
Facilitates conditional inquiries by doing the work of an
IF-THEN-ELSE statement:
SELECT last_name, job_id, salary,
CASE job_id WHEN 'IT_PROG' THEN 1.10*salary
WHEN 'ST_CLERK' THEN 1.15*salary
WHEN 'SA_REP'
THEN 1.20*salary
ELSE
salary END
"REVISED_SALARY"
FROM
employees;
…
…
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Copyright © 2009, Oracle. All rights reserved.
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Using the CASE Expression
In the SQL statement in the slide, the value of JOB_ID is decoded. If JOB_ID is IT_PROG, the
salary increase is 10%; if JOB_ID is ST_CLERK, the salary increase is 15%; if JOB_ID is
SA_REP, the salary increase is 20%. For all other job roles, there is no increase in salary.
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The same statement can be written with the DECODE function.
The following code is an example of the searched CASE expression. In a searched CASE expression,
the search occurs from left to right until an occurrence of the listed condition is found, and then it
returns the return expression. If no condition is found to be true, and if an ELSE clause exists, the
return expression in the ELSE clause is returned; otherwise, a NULL is returned.
SELECT last_name,salary,
(CASE WHEN salary<5000 THEN 'Low'
WHEN salary<10000 THEN 'Medium'
WHEN salary<20000 THEN 'Good'
ELSE 'Excellent'
END) qualified_salary
FROM employees;
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Oracle Database 11g: SQL Fundamentals I 4 - 38
DECODE Function
Facilitates conditional inquiries by doing the work of a CASE
expression or an IF-THEN-ELSE statement:
DECODE(col|expression, search1, result1
[, search2, result2,...,]
[, default])
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DECODE Function
The DECODE function decodes an expression in a way similar to the IF-THEN-ELSE logic that is
used in various languages. The DECODE function decodes expression after comparing it to each
search value. If the expression is the same as search, result is returned.
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If the default value is omitted, a null value is returned where a search value does not match any of the
result values.
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Oracle Database 11g: SQL Fundamentals I 4 - 39
Using the DECODE Function
SELECT last_name, job_id, salary,
DECODE(job_id, 'IT_PROG', 1.10*salary,
'ST_CLERK', 1.15*salary,
'SA_REP',
1.20*salary,
salary)
REVISED_SALARY
FROM
employees;
…
…
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Using the DECODE Function
In the SQL statement in the slide, the value of JOB_ID is tested. If JOB_ID is IT_PROG, the salary
increase is 10%; if JOB_ID is ST_CLERK, the salary increase is 15%; if JOB_ID is SA_REP, the
salary increase is 20%. For all other job roles, there is no increase in salary.
The same statement can be expressed in pseudocode as an IF-THEN-ELSE statement:
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IF job_id =
IF job_id =
IF job_id =
ELSE salary
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'IT_PROG'
'ST_CLERK'
'SA_REP'
= salary
THEN
THEN
THEN
salary = salary*1.10
salary = salary*1.15
salary = salary*1.20
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Oracle Database 11g: SQL Fundamentals I 4 - 40
Using the DECODE Function
Display the applicable tax rate for each employee in
department 80:
SELECT last_name, salary,
DECODE (TRUNC(salary/2000, 0),
0, 0.00,
1, 0.09,
2, 0.20,
3, 0.30,
4, 0.40,
5, 0.42,
6, 0.44,
0.45) TAX_RATE
FROM
employees
WHERE department_id = 80;
Copyright © 2009, Oracle. All rights reserved.
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Using the DECODE Function (continued)
This slide shows another example using the DECODE function. In this example, you determine the
tax rate for each employee in department 80 based on the monthly salary. The tax rates are as
follows:
Monthly Salary Range
Tax Rate
$0.00–1,999.99
00%
$2,000.00–3,999.99
09%
$4,000.00–5,999.99
20%
$6,000.00–7,999.99
30%
$8,000.00–9,999.99
40%
$10,000.00–11,999.99
42%
$12,200.00–13,999.99
44%
$14,000.00 or greater
45%
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Oracle Database 11g: SQL Fundamentals I 4 - 41
Quiz
The TO_NUMBER function converts either character strings or
date values to a number in the format specified by the optional
format model.
1. True
2. False
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Answer: 2
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Oracle Database 11g: SQL Fundamentals I 4 - 42
Summary
In this lesson, you should have learned how to:
• Alter date formats for display using functions
• Convert column data types using functions
• Use NVL functions
• Use IF-THEN-ELSE logic and other conditional
expressions in a SELECT statement
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Summary
Remember the following:
• Conversion functions can convert character, date, and numeric values: TO_CHAR, TO_DATE,
TO_NUMBER
• There are several functions that pertain to nulls, including NVL, NVL2, NULLIF, and
COALESCE.
• IF-THEN-ELSE logic can be applied within a SQL statement by using the CASE expression or
the DECODE function.
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Oracle Database 11g: SQL Fundamentals I 4 - 43
Practice 4: Overview
This practice covers the following topics:
• Creating queries that use TO_CHAR, TO_DATE, and other
DATE functions
•
Creating queries that use conditional expressions such as
DECODE and CASE
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Practice 4: Overview
This practice provides a variety of exercises using TO_CHAR and TO_DATE functions, and
conditional expressions such as DECODE and CASE. Remember that for nested functions, the results
are evaluated from the innermost function to the outermost function.
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Oracle Database 11g: SQL Fundamentals I 4 - 44
Practice 4
1. Create a report that produces the following for each employee:
earns monthly but wants <3 times
salary.>. Label the column Dream Salaries.
…
2. Display each employee’s last name, hire date, and salary review date, which is the first Monday
after six months of service. Label the column REVIEW. Format the dates to appear in the format
similar to “Monday, the Thirty-First of July, 2000.”
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Oracle Database 11g: SQL Fundamentals I 4 - 45
Practice 4 (continued)
3. Display the last name, hire date, and day of the week on which the employee started. Label the
column DAY. Order the results by the day of the week, starting with Monday.
…
4. Create a query that displays the employees’ last names and commission amounts. If an employee
does not earn commission, show “No Commission.” Label the column COMM.
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Oracle Database 11g: SQL Fundamentals I 4 - 46
Practice 4 (continued)
If you have time, complete the following exercises:
5. Using the DECODE function, write a query that displays the grade of all employees based on the
value of the column JOB_ID, using the following data:
Job
AD_PRES
ST_MAN
IT_PROG
SA_REP
ST_CLERK
None of the above
Grade
A
B
C
D
E
0
…
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6. Rewrite the statement in the preceding exercise using the CASE syntax.
…
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Oracle Database 11g: SQL Fundamentals I 4 - 47
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Reporting Aggregated Data
Using the Group Functions
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Objectives
After completing this lesson, you should be able to do the
following:
• Identify the available group functions
• Describe the use of group functions
• Group data by using the GROUP BY clause
• Include or exclude grouped rows by using the HAVING
clause
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Objectives
This lesson further addresses functions. It focuses on obtaining summary information (such as
averages) for groups of rows. It discusses how to group rows in a table into smaller sets and how to
specify search criteria for groups of rows.
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Oracle Database 11g: SQL Fundamentals I 5 - 2
Lesson Agenda
•
Group functions:
–
–
–
–
•
Types and syntax
Use AVG, SUM, MIN, MAX, COUNT
Use DISTINCT keyword within group functions
NULL values in a group function
Grouping rows:
– GROUP BY clause
– HAVING clause
•
Nesting group functions
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Oracle Database 11g: SQL Fundamentals I 5 - 3
What Are Group Functions?
Group functions operate on sets of rows to give one result per
group.
EMPLOYEES
Maximum salary in
EMPLOYEES table
…
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What Are Group Functions?
Unlike single-row functions, group functions operate on sets of rows to give one result per group.
These sets may comprise the entire table or the table split into groups.
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Oracle Database 11g: SQL Fundamentals I 5 - 4
Types of Group Functions
•
•
•
•
•
•
•
AVG
COUNT
MAX
MIN
STDDEV
SUM
VARIANCE
Group
functions
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Types of Group Functions
Each of the functions accepts an argument. The following table identifies the options that you can
use in the syntax:
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Function
AVG([DISTINCT|ALL]n)
COUNT({*|[DISTINCT|ALL]expr
})
MAX([DISTINCT|ALL]expr)
MIN([DISTINCT|ALL]expr)
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STDDEV([DISTINCT|ALL]x)
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SUM([DISTINCT|ALL]n)
O
VARIANCE([DISTINCT|ALL]x)
Description
Average value of n, ignoring null values
Number of rows, where expr evaluates to
something other than null (count all selected
rows using *, including duplicates and rows
with nulls)
Maximum value of expr, ignoring null values
Minimum value of expr, ignoring null values
Standard deviation of n, ignoring null values
Sum values of n, ignoring null values
Variance of n, ignoring null values
Oracle Database 11g: SQL Fundamentals I 5 - 5
Group Functions: Syntax
SELECT
FROM
[WHERE
[ORDER BY
group_function(column), ...
table
condition]
column];
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Group Functions: Syntax
The group function is placed after the SELECT keyword. You may have multiple group functions
separated by commas.
Guidelines for using the group functions:
• DISTINCT makes the function consider only nonduplicate values; ALL makes it consider every
value, including duplicates. The default is ALL and therefore does not need to be specified.
• The data types for the functions with an expr argument may be CHAR, VARCHAR2, NUMBER,
or DATE.
• All group functions ignore null values. To substitute a value for null values, use the NVL, NVL2,
or COALESCE functions.
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Oracle Database 11g: SQL Fundamentals I 5 - 6
Using the AVG and SUM Functions
You can use AVG and SUM for numeric data.
SELECT AVG(salary), MAX(salary),
MIN(salary), SUM(salary)
FROM
employees
WHERE job_id LIKE '%REP%';
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Using the AVG and SUM Functions
You can use the AVG, SUM, MIN, and MAX functions against the columns that can store numeric data.
The example in the slide displays the average, highest, lowest, and sum of monthly salaries for all
sales representatives.
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Oracle Database 11g: SQL Fundamentals I 5 - 7
Using the MIN and MAX Functions
You can use MIN and MAX for numeric, character, and date
data types.
SELECT MIN(hire_date), MAX(hire_date)
FROM
employees;
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Using the MIN and MAX Functions
You can use the MAX and MIN functions for numeric, character, and date data types. The example in
the slide displays the most junior and most senior employees.
The following example displays the employee last name that is first and the employee last name that
is last in an alphabetic list of all employees:
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SELECT MIN(last_name), MAX(last_name)
FROM
employees;
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Note: The AVG, SUM, VARIANCE, and STDDEV functions can be used only with numeric data types.
MAX and MIN cannot be used with LOB or LONG data types.
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Oracle Database 11g: SQL Fundamentals I 5 - 8
Using the COUNT Function
COUNT(*) returns the number of rows in a table:
1
SELECT COUNT(*)
FROM
employees
WHERE department_id = 50;
COUNT(expr) returns the number of rows with non-null values
for expr:
2
SELECT COUNT(commission_pct)
FROM
employees
WHERE department_id = 80;
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Using the COUNT Function
The COUNT function has three formats:
• COUNT(*)
• COUNT(expr)
• COUNT(DISTINCT expr)
COUNT(*) returns the number of rows in a table that satisfy the criteria of the SELECT statement,
including duplicate rows and rows containing null values in any of the columns. If a WHERE clause is
included in the SELECT statement, COUNT(*) returns the number of rows that satisfy the condition
in the WHERE clause.
In contrast, COUNT(expr) returns the number of non-null values that are in the column identified
by expr.
COUNT(DISTINCT expr) returns the number of unique, non-null values that are in the column
identified by expr.
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Examples:
1. The example in the slide displays the number of employees in department 50.
2. The example in the slide displays the number of employees in department 80 who can earn a
commission.
Oracle Database 11g: SQL Fundamentals I 5 - 9
Using the DISTINCT Keyword
•
COUNT(DISTINCT expr) returns the number of distinct
non-null values of expr.
•
To display the number of distinct department values in the
EMPLOYEES table:
SELECT COUNT(DISTINCT department_id)
FROM
employees;
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Using the DISTINCT Keyword
Use the DISTINCT keyword to suppress the counting of any duplicate values in a column.
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The example in the slide displays the number of distinct department values that are in the
EMPLOYEES table.
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Oracle Database 11g: SQL Fundamentals I 5 - 10
Group Functions and Null Values
Group functions ignore null values in the column:
1
SELECT AVG(commission_pct)
FROM
employees;
The NVL function forces group functions to include null values:
2
SELECT AVG(NVL(commission_pct, 0))
FROM
employees;
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Group Functions and Null Values
All group functions ignore null values in the column.
However, the NVL function forces group functions to include null values.
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Examples:
1. The average is calculated based on only those rows in the table in which a valid value is stored
in the COMMISSION_PCT column. The average is calculated as the total commission that is
paid to all employees divided by the number of employees receiving a commission (four).
2. The average is calculated based on all rows in the table, regardless of whether null values are
stored in the COMMISSION_PCT column. The average is calculated as the total commission
that is paid to all employees divided by the total number of employees in the company (20).
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Oracle Database 11g: SQL Fundamentals I 5 - 11
Lesson Agenda
•
Group functions:
–
–
–
–
•
Types and syntax
Use AVG, SUM, MIN, MAX, COUNT
Use DISTINCT keyword within group functions
NULL values in a group function
Grouping rows:
– GROUP BY clause
– HAVING clause
•
Nesting group functions
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Oracle Database 11g: SQL Fundamentals I 5 - 12
Creating Groups of Data
EMPLOYEES
4400
9500
Average salary in
EMPLOYEES table for
each department
3500
6400
10033
…
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Creating Groups of Data
Until this point in our discussion, all group functions have treated the table as one large group of
information. At times, however, you need to divide the table of information into smaller groups. This
can be done by using the GROUP BY clause.
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Oracle Database 11g: SQL Fundamentals I 5 - 13
Creating Groups of Data:
GROUP BY Clause Syntax
SELECT
column, group_function(column)
FROM
table
[WHERE
condition]
[GROUP BY group_by_expression]
[ORDER BY column];
You can divide rows in a table into smaller groups by using the
GROUP BY clause.
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Creating Groups of Data: GROUP BY Clause Syntax
You can use the GROUP BY clause to divide the rows in a table into groups. You can then use the
group functions to return summary information for each group.
In the syntax:
group_by_expression
specifies columns whose values determine the basis for
grouping rows
Guidelines
• If you include a group function in a SELECT clause, you cannot select individual results as well,
unless the individual column appears in the GROUP BY clause. You receive an error message if
you fail to include the column list in the GROUP BY clause.
• Using a WHERE clause, you can exclude rows before dividing them into groups.
• You must include the columns in the GROUP BY clause.
• You cannot use a column alias in the GROUP BY clause.
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Oracle Database 11g: SQL Fundamentals I 5 - 14
Using the GROUP BY Clause
All columns in the SELECT list that are not in group functions
must be in the GROUP BY clause.
SELECT
department_id, AVG(salary)
FROM
employees
GROUP BY department_id ;
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Using the GROUP BY Clause
When using the GROUP BY clause, make sure that all columns in the SELECT list that are not group
functions are included in the GROUP BY clause. The example in the slide displays the department
number and the average salary for each department. Here is how this SELECT statement, containing
a GROUP BY clause, is evaluated:
• The SELECT clause specifies the columns to be retrieved, as follows:
- Department number column in the EMPLOYEES table
- The average of all salaries in the group that you specified in the GROUP BY clause
• The FROM clause specifies the tables that the database must access: the EMPLOYEES table
• The WHERE clause specifies the rows to be retrieved. Because there is no WHERE clause, all
rows are retrieved by default.
• The GROUP BY clause specifies how the rows should be grouped. The rows are grouped by
department number, so the AVG function that is applied to the salary column calculates the
average salary for each department.
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Oracle Database 11g: SQL Fundamentals I 5 - 15
Using the GROUP BY Clause
The GROUP BY column does not have to be in the SELECT list.
SELECT
AVG(salary)
FROM
employees
GROUP BY department_id ;
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Using the GROUP BY Clause (continued)
The GROUP BY column does not have to be in the SELECT clause. For example, the SELECT
statement in the slide displays the average salaries for each department without displaying the
respective department numbers. Without the department numbers, however, the results do not look
meaningful.
You can also use the group function in the ORDER BY clause:
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SELECT
FROM
GROUP BY
ORDER BY
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department_id, AVG(salary)
employees
department_id
AVG(salary);
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Oracle Database 11g: SQL Fundamentals I 5 - 16
Grouping by More than One Column
Add the salaries in the EMPLOYEES
table for each job, grouped by
department.
EMPLOYEES
…
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Grouping by More than One Column
Sometimes, you need to see results for groups within groups. The slide shows a report that displays
the total salary that is paid to each job title in each department.
The EMPLOYEES table is grouped first by the department number, and then by the job title within
that grouping. For example, the four stock clerks in department 50 are grouped together, and a single
result (total salary) is produced for all stock clerks in the group.
The following SELECT statement returns the result shown in the slide:
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SELECT
FROM
GROUP BY
ORDER BY
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department_id, job_id, sum(salary)
employees
department_id, job_id
job_id;
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Oracle Database 11g: SQL Fundamentals I 5 - 17
Using the GROUP BY Clause
on Multiple Columns
SELECT
FROM
WHERE
GROUP BY
ORDER BY
department_id, job_id, SUM(salary)
employees
department_id > 40
department_id, job_id
department_id;
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Using the Group By Clause on Multiple Columns
You can return summary results for groups and subgroups by listing multiple GROUP BY columns.
The GROUP BY clause groups rows but does not guarantee the order of the result set. To order the
groupings, use the ORDER BY clause.
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In the example in the slide, the SELECT statement that contains a GROUP BY clause is evaluated as
follows:
• The SELECT clause specifies the column to be retrieved:
- Department ID in the EMPLOYEES table
- Job ID in the EMPLOYEES table
- The sum of all salaries in the group that you specified in the GROUP BY clause
• The FROM clause specifies the tables that the database must access: the EMPLOYEES table.
• The WHERE clause reduces the result set to those rows where department ID is greater than 40.
• The GROUP BY clause specifies how you must group the resulting rows:
- First, the rows are grouped by the department ID.
- Second, the rows are grouped by job ID in the department ID groups.
• The ORDER BY clause sorts the results by department ID.
Notes: The SUM function is applied to the salary column for all job IDs in the result set in each
department ID group. Also, note that the SA_REP row is not returned. The department ID for this
row is NULL, and therefore, does not meet the WHERE condition.
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Oracle Database 11g: SQL Fundamentals I 5 - 18
Illegal Queries
Using Group Functions
Any column or expression in the SELECT list that is not an
aggregate function must be in the GROUP BY clause:
SELECT department_id, COUNT(last_name)
FROM
employees;
A GROUP BY clause must be added to
count the last names for each
department_id.
SELECT department_id, job_id, COUNT(last_name)
FROM
employees
GROUP BY department_id;
Either add job_id in the GROUP BY or
remove the job_id column from the
SELECT list.
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Illegal Queries Using Group Functions
Whenever you use a mixture of individual items (DEPARTMENT_ID) and group functions (COUNT)
in the same SELECT statement, you must include a GROUP BY clause that specifies the individual
items (in this case, DEPARTMENT_ID). If the GROUP BY clause is missing, then the error message
“not a single-group group function” appears and an asterisk (*) points to the offending column. You
can correct the error in the first example in the slide by adding the GROUP BY clause:
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SELECT
department_id, count(last_name)
FROM
employees
GROUP BY department_id;
Any column or expression in the SELECT list that is not an aggregate function must be in the GROUP
BY clause. In the second example in the slide, job_id is neither in the GROUP BY clause nor is it
being used by a group function, so there is a “not a GROUP BY expression” error. You can correct the
error in the second slide example by adding job_id in the GROUP BY clause.
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SELECT department_id, job_id, COUNT(last_name)
FROM
employees
GROUP BY department_id, job_id;
Oracle Database 11g: SQL Fundamentals I 5 - 19
Illegal Queries
Using Group Functions
•
•
•
You cannot use the WHERE clause to restrict groups.
You use the HAVING clause to restrict groups.
You cannot use group functions in the WHERE clause.
SELECT
FROM
WHERE
GROUP BY
department_id, AVG(salary)
employees
AVG(salary) > 8000
department_id;
Cannot use the
WHERE clause to
restrict groups
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Illegal Queries Using Group Functions (continued)
The WHERE clause cannot be used to restrict groups. The SELECT statement in the example in the
slide results in an error because it uses the WHERE clause to restrict the display of the average salaries
of those departments that have an average salary greater than $8,000.
However, you can correct the error in the example by using the HAVING clause to restrict groups:
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SELECT
FROM
GROUP BY
HAVING
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department_id, AVG(salary)
employees
department_id
AVG(salary) > 8000;
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Oracle Database 11g: SQL Fundamentals I 5 - 20
Restricting Group Results
EMPLOYEES
The maximum salary per
department when it is
greater than $10,000
…
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Restricting Group Results
You use the HAVING clause to restrict groups in the same way that you use the WHERE clause to
restrict the rows that you select. To find the maximum salary in each of the departments that have a
maximum salary greater than $10,000, you need to do the following:
1. Find the average salary for each department by grouping by department number.
2. Restrict the groups to those departments with a maximum salary greater than $10,000.
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Oracle Database 11g: SQL Fundamentals I 5 - 21
Restricting Group Results
with the HAVING Clause
When you use the HAVING clause, the Oracle server restricts
groups as follows:
1. Rows are grouped.
2. The group function is applied.
3. Groups matching the HAVING clause are displayed.
SELECT
FROM
[WHERE
[GROUP BY
[HAVING
[ORDER BY
column, group_function
table
condition]
group_by_expression]
group_condition]
column];
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Restricting Group Results with the HAVING Clause
You use the HAVING clause to specify the groups that are to be displayed, thus further restricting the
groups on the basis of aggregate information.
In the syntax, group_condition restricts the groups of rows returned to those groups for which
the specified condition is true.
The Oracle server performs the following steps when you use the HAVING clause:
1. Rows are grouped.
2. The group function is applied to the group.
3. The groups that match the criteria in the HAVING clause are displayed.
The HAVING clause can precede the GROUP BY clause, but it is recommended that you place the
GROUP BY clause first because it is more logical. Groups are formed and group functions are
calculated before the HAVING clause is applied to the groups in the SELECT list.
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Oracle Database 11g: SQL Fundamentals I 5 - 22
Using the HAVING Clause
SELECT
FROM
GROUP BY
HAVING
department_id, MAX(salary)
employees
department_id
MAX(salary)>10000 ;
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Copyright © 2009, Oracle. All rights reserved.
Using the HAVING Clause
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The example in the slide displays the department numbers and maximum salaries for those
departments with a maximum salary greater than $10,000.
You can use the GROUP BY clause without using a group function in the SELECT list. If you restrict
rows based on the result of a group function, you must have a GROUP BY clause as well as the
HAVING clause.
The following example displays the department numbers and average salaries for those departments
with a maximum salary greater than $10,000:
SELECT
FROM
GROUP BY
HAVING
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department_id, AVG(salary)
employees
department_id
max(salary)>10000;
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Oracle Database 11g: SQL Fundamentals I 5 - 23
Using the HAVING Clause
SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY
job_id, SUM(salary) PAYROLL
employees
job_id NOT LIKE '%REP%'
job_id
SUM(salary) > 13000
SUM(salary);
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Copyright © 2009, Oracle. All rights reserved.
Using the HAVING Clause (continued)
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The example in the slide displays the job ID and total monthly salary for each job that has a total
payroll exceeding $13,000. The example excludes sales representatives and sorts the list by the total
monthly salary.
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Oracle Database 11g: SQL Fundamentals I 5 - 24
Lesson Agenda
•
Group functions:
–
–
–
–
•
Types and syntax
Use AVG, SUM, MIN, MAX, COUNT
Use DISTINCT keyword within group functions
NULL values in a group function
Grouping rows:
– GROUP BY clause
– HAVING clause
•
Nesting group functions
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Oracle Database 11g: SQL Fundamentals I 5 - 25
Nesting Group Functions
Display the maximum average salary:
SELECT
MAX(AVG(salary))
FROM
employees
GROUP BY department_id;
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Nesting Group Functions
Group functions can be nested to a depth of two functions. The example in the slide calculates the
average salary for each department_id and then displays the maximum average salary.
Note that GROUP BY clause is mandatory when nesting group functions.
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Oracle Database 11g: SQL Fundamentals I 5 - 26
Quiz
Identify the guidelines for group functions and the GROUP BY
clause.
1. You cannot use a column alias in the GROUP BY clause.
2. The GROUP BY column must be in the SELECT clause.
3. By using a WHERE clause, you can exclude rows before
dividing them into groups.
4. The GROUP BY clause groups rows and ensures order of
the result set.
5. If you include a group function in a SELECT clause, you
cannot select individual results as well.
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Copyright © 2009, Oracle. All rights reserved.
Answer: 1, 3
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Oracle Database 11g: SQL Fundamentals I 5 - 27
Summary
In this lesson, you should have learned how to:
• Use the group functions COUNT, MAX, MIN, SUM, and AVG
• Write queries that use the GROUP BY clause
• Write queries that use the HAVING clause
SELECT
FROM
[WHERE
[GROUP BY
[HAVING
[ORDER BY
column, group_function
table
condition]
group_by_expression]
group_condition]
column];
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Summary
There are several group functions available in SQL, such as:
AVG, COUNT, MAX, MIN, SUM, STDDEV, and VARIANCE
You can create subgroups by using the GROUP BY clause. Further, groups can be restricted using the
HAVING clause.
Place the HAVING and GROUP BY clauses after the WHERE clause in a statement. The order of the
GROUP BY and HAVING clauses following the WHERE clause is not important. Place the ORDER BY
clause at the end.
The Oracle server evaluates the clauses in the following order:
1. If the statement contains a WHERE clause, the server establishes the candidate rows.
2. The server identifies the groups that are specified in the GROUP BY clause.
3. The HAVING clause further restricts result groups that do not meet the group criteria in the
HAVING clause.
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Note: For a complete list of the group functions, see Oracle Database SQL Language Reference 11g,
Release 1 (11.1).
Oracle Database 11g: SQL Fundamentals I 5 - 28
Practice 5: Overview
This practice covers the following topics:
• Writing queries that use the group functions
• Grouping by rows to achieve more than one result
• Restricting groups by using the HAVING clause
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Practice 5: Overview
At the end of this practice, you should be familiar with using group functions and selecting groups of
data.
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Oracle Database 11g: SQL Fundamentals I 5 - 29
Practice 5
Determine the validity of the following three statements. Circle either True or False.
1. Group functions work across many rows to produce one result per group.
True/False
2. Group functions include nulls in calculations.
True/False
3. The WHERE clause restricts rows before inclusion in a group calculation.
True/False
The HR department needs the following reports:
4. Find the highest, lowest, sum, and average salary of all employees. Label the columns
as Maximum, Minimum, Sum, and Average, respectively. Round your results to the nearest
whole number. Save your SQL statement as lab_05_04.sql. Run the query.
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5. Modify the query in lab_05_04.sql to display the minimum, maximum, sum, and average
salary for each job type. Resave lab_05_04.sql as lab_05_05.sql. Run the statement
in lab_05_05.sql.
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Oracle Database 11g: SQL Fundamentals I 5 - 30
Practice 5 (continued)
6. Write a query to display the number of people with the same job.
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Generalize the query so that the user in the HR department is prompted for a job title. Save the script
to a file named lab_05_06.sql. Run the query. Enter IT_PROG when prompted.
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7. Determine the number of managers without listing them. Label the column as Number of
Managers. Hint: Use the MANAGER_ID column to determine the number of managers.
8. Find the difference between the highest and lowest salaries. Label the column DIFFERENCE.
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Oracle Database 11g: SQL Fundamentals I 5 - 31
Practice 5 (continued)
If you have time, complete the following exercises:
9. Create a report to display the manager number and the salary of the lowest-paid employee for
that manager. Exclude anyone whose manager is not known. Exclude any groups where the
minimum salary is $6,000 or less. Sort the output in descending order of salary.
If you want an extra challenge, complete the following exercises:
10. Create a query to display the total number of employees and, of that total, the number of
employees hired in 1995, 1996, 1997, and 1998. Create appropriate column headings.
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11. Create a matrix query to display the job, the salary for that job based on department number,
and the total salary for that job, for departments 20, 50, 80, and 90, giving each column an
appropriate heading.
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Oracle Database 11g: SQL Fundamentals I 5 - 32
Displaying Data
from Multiple Tables
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Objectives
After completing this lesson, you should be able to do the
following:
• Write SELECT statements to access data from more than
one table using equijoins and nonequijoins
• Join a table to itself by using a self-join
• View data that generally does not meet a join condition by
using OUTER joins
•
Generate a Cartesian product of all rows from two or more
tables
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Objectives
This lesson explains how to obtain data from more than one table. A join is used to view information
from multiple tables. Therefore, you can join tables together to view information from more than one
table.
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Note: Information on joins is found in the section on SQL Queries and Subqueries: Joins in
Oracle Database SQL Language Reference 11g, Release 1 (11.1).
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Oracle Database 11g: SQL Fundamentals I 6 - 2
Lesson Agenda
•
Types of JOINS and its syntax
•
Natural join:
– USING clause
– ON clause
•
•
•
Self-join
Nonequijoins
OUTER join:
– LEFT OUTER join
– RIGHT OUTER join
– FULL OUTER join
•
Cartesian product
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– Cross join
Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 6 - 3
Obtaining Data from Multiple Tables
EMPLOYEES
DEPARTMENTS
…
…
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Obtaining Data from Multiple Tables
Sometimes you need to use data from more than one table. In the example in the slide, the report
displays data from two separate tables:
• Employee IDs exist in the EMPLOYEES table.
• Department IDs exist in both the EMPLOYEES and DEPARTMENTS tables.
• Department names exist in the DEPARTMENTS table.
To produce the report, you need to link the EMPLOYEES and DEPARTMENTS tables, and access data
from both of them.
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Oracle Database 11g: SQL Fundamentals I 6 - 4
Types of Joins
Joins that are compliant with the SQL:1999 standard include
the following:
• Natural joins:
– NATURAL JOIN clause
– USING clause
– ON clause
•
OUTER joins:
– LEFT OUTER JOIN
– RIGHT OUTER JOIN
– FULL OUTER JOIN
•
Cross joins
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Types of Joins
To join tables, you can use a join syntax that is compliant with the SQL:1999 standard.
Note
• Before the Oracle9i release, the join syntax was different from the American National Standards
Institute (ANSI) standards. The SQL:1999–compliant join syntax does not offer any
performance benefits over the Oracle-proprietary join syntax that existed in the prior releases.
For detailed information about the proprietary join syntax, see Appendix C: Oracle Join Syntax.
• The following slide discusses the SQL:1999 join syntax.
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Oracle Database 11g: SQL Fundamentals I 6 - 5
Joining Tables Using SQL:1999 Syntax
Use a join to query data from more than one table:
SELECT
table1.column, table2.column
FROM
table1
[NATURAL JOIN table2] |
[JOIN table2 USING (column_name)] |
[JOIN table2
ON (table1.column_name = table2.column_name)]|
[LEFT|RIGHT|FULL OUTER JOIN table2
ON (table1.column_name = table2.column_name)]|
[CROSS JOIN table2];
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Joining Tables Using SQL:1999 Syntax
In the syntax:
table1.column denotes the table and the column from which data is retrieved
NATURAL JOIN joins two tables based on the same column name
JOIN table2 USING column_name performs an equijoin based on the column name
JOIN table2 ON table1.column_name = table2.column_name performs an equijoin
based on the condition in the ON clause
LEFT/RIGHT/FULL OUTER is used to perform OUTER joins
CROSS JOIN returns a Cartesian product from the two tables
For more information, see the section titled SELECT in Oracle Database SQL Language Reference
11g, Release 1 (11.1).
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Oracle Database 11g: SQL Fundamentals I 6 - 6
Qualifying Ambiguous
Column Names
•
•
•
•
Use table prefixes to qualify column names that are in
multiple tables.
Use table prefixes to improve performance.
Instead of full table name prefixes, use table aliases.
Table alias gives a table a shorter name:
– Keeps SQL code smaller, uses less memory
•
Use column aliases to distinguish columns that have
identical names, but reside in different tables.
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Qualifying Ambiguous Column Names
When joining two or more tables, you need to qualify the names of the columns with the table name
to avoid ambiguity. Without the table prefixes, the DEPARTMENT_ID column in the SELECT list
could be from either the DEPARTMENTS table or the EMPLOYEES table. It is necessary to add the
table prefix to execute your query. If there are no common column names between the two tables,
there is no need to qualify the columns. However, using the table prefix improves performance,
because you tell the Oracle server exactly where to find the columns.
However, qualifying column names with table names can be time consuming, particularly if the table
names are lengthy. Instead, you can use table aliases. Just as a column alias gives a column another
name, a table alias gives a table another name. Table aliases help to keep SQL code smaller,
therefore using less memory.
The table name is specified in full, followed by a space and then the table alias. For example, the
EMPLOYEES table can be given an alias of e, and the DEPARTMENTS table an alias of d.
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Guidelines
• Table aliases can be up to 30 characters in length, but shorter aliases are better than longer ones.
• If a table alias is used for a particular table name in the FROM clause, then that table alias must
be substituted for the table name throughout the SELECT statement.
• Table aliases should be meaningful.
• The table alias is valid for only the current SELECT statement.
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Oracle Database 11g: SQL Fundamentals I 6 - 7
Lesson Agenda
•
Types of JOINS and its syntax
•
Natural join:
– USING clause
– ON clause
•
•
•
Self-join
Nonequijoins
OUTER join:
– LEFT OUTER join
– RIGHT OUTER join
– FULL OUTER join
•
Cartesian product
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– Cross join
Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 6 - 8
Creating Natural Joins
•
•
The NATURAL JOIN clause is based on all columns in the
two tables that have the same name.
It selects rows from the two tables that have equal values
in all matched columns.
If the columns having the same names have different data
types, an error is returned.
•
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Creating Natural Joins
You can join tables automatically based on the columns in the two tables that have matching data
types and names. You do this by using the NATURAL JOIN keywords.
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Note: The join can happen on only those columns that have the same names and data types in both
tables. If the columns have the same name but different data types, then the NATURAL JOIN syntax
causes an error.
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Oracle Database 11g: SQL Fundamentals I 6 - 9
Retrieving Records with Natural Joins
SELECT department_id, department_name,
location_id, city
FROM
departments
NATURAL JOIN locations ;
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Retrieving Records with Natural Joins
In the example in the slide, the LOCATIONS table is joined to the DEPARTMENT table by the
LOCATION_ID column, which is the only column of the same name in both tables. If other common
columns were present, the join would have used them all.
Natural Joins with a WHERE Clause
Additional restrictions on a natural join are implemented by using a WHERE clause. The following
example limits the rows of output to those with a department ID equal to 20 or 50:
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SELECT
department_id, department_name,
location_id, city
FROM
departments
NATURAL JOIN locations
WHERE
department_id IN (20, 50);
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Oracle Database 11g: SQL Fundamentals I 6 - 10
Creating Joins with the USING Clause
•
•
If several columns have the same names but the data
types do not match, use the USING clause to specify the
columns for the equijoin.
Use the USING clause to match only one column when
more than one column matches.
The NATURAL JOIN and USING clauses are mutually
exclusive.
•
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Creating Joins with the USING Clause
Natural joins use all columns with matching names and data types to join the tables. The USING
clause can be used to specify only those columns that should be used for an equijoin.
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Oracle Database 11g: SQL Fundamentals I 6 - 11
Joining Column Names
DEPARTMENTS
EMPLOYEES
Primary key
…
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Foreign key
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Joining Column Names
To determine an employee’s department name, you compare the value in the DEPARTMENT_ID
column in the EMPLOYEES table with the DEPARTMENT_ID values in the DEPARTMENTS table.
The relationship between the EMPLOYEES and DEPARTMENTS tables is an equijoin; that is, values
in the DEPARTMENT_ID column in both the tables must be equal. Frequently, this type of join
involves primary and foreign key complements.
Note: Equijoins are also called simple joins or inner joins.
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Oracle Database 11g: SQL Fundamentals I 6 - 12
Retrieving Records with the USING Clause
SELECT employee_id, last_name,
location_id, department_id
FROM
employees JOIN departments
USING (department_id) ;
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Copyright © 2009, Oracle. All rights reserved.
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Retrieving Records with the USING Clause
In the example in the slide, the DEPARTMENT_ID columns in the EMPLOYEES and
DEPARTMENTS tables are joined and thus the LOCATION_ID of the department where an
employee works is shown.
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Oracle Database 11g: SQL Fundamentals I 6 - 13
Using Table Aliases with the USING Clause
•
Do not qualify a column that is used in the USING clause.
•
If the same column is used elsewhere in the SQL
statement, do not alias it.
SELECT l.city, d.department_name
FROM
locations l JOIN departments d
USING (location_id)
WHERE d.location_id = 1400;
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Using Table Aliases with the USING clause
When joining with the USING clause, you cannot qualify a column that is used in the USING clause
itself. Furthermore, if that column is used anywhere in the SQL statement, you cannot alias it. For
example, in the query mentioned in the slide, you should not alias the location_id column in the
WHERE clause because the column is used in the USING clause.
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The columns that are referenced in the USING clause should not have a qualifier (table name or
alias) anywhere in the SQL statement. For example, the following statement is valid:
SELECT l.city, d.department_name
FROM
locations l JOIN departments d USING (location_id)
WHERE location_id = 1400;
Because, other columns that are common in both the tables, but not used in the USING clause, must
be prefixed with a table alias otherwise you get the “column ambiguously defined” error.
In the following statement, manager_id is present in both the employees and departments
table and if manager_id is not prefixed with a table alias, it gives a “column ambiguously
defined” error.
The following statement is valid:
SELECT first_name, d.department_name, d.manager_id
FROM
employees e JOIN departments d USING (department_id)
WHERE department_id = 50;
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Oracle Database 11g: SQL Fundamentals I 6 - 14
Creating Joins with the ON Clause
•
•
The join condition for the natural join is basically an
equijoin of all columns with the same name.
Use the ON clause to specify arbitrary conditions or specify
columns to join.
The join condition is separated from other search
conditions.
The ON clause makes code easy to understand.
•
•
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Creating Joins with the ON Clause
Use the ON clause to specify a join condition. With this, you can specify join conditions separate
from any search or filter conditions in the WHERE clause.
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Oracle Database 11g: SQL Fundamentals I 6 - 15
Retrieving Records with the ON Clause
SELECT e.employee_id, e.last_name, e.department_id,
d.department_id, d.location_id
FROM
employees e JOIN departments d
ON
(e.department_id = d.department_id);
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Copyright © 2009, Oracle. All rights reserved.
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Retrieving Records with the ON Clause
In this example, the DEPARTMENT_ID columns in the EMPLOYEES and DEPARTMENTS table are
joined using the ON clause. Wherever a department ID in the EMPLOYEES table equals a department
ID in the DEPARTMENTS table, the row is returned. The table alias is necessary to qualify the
matching column_names.
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You can also use the ON clause to join columns that have different names. The parenthesis around
the joined columns as in the slide example, (e.department_id = d.department_id) is
optional. So, even ON e.department_id = d.department_id will work.
Note: SQL Developer suffixes a ‘_1’ to differentiate between the two department_ids.
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Oracle Database 11g: SQL Fundamentals I 6 - 16
Creating Three-Way Joins with
the ON Clause
SELECT
FROM
JOIN
ON
JOIN
ON
employee_id, city, department_name
employees e
departments d
d.department_id = e.department_id
locations l
d.location_id = l.location_id;
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Copyright © 2009, Oracle. All rights reserved.
Creating Three-Way Joins with the ON Clause
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A three-way join is a join of three tables. In SQL:1999–compliant syntax, joins are performed from
left to right. So, the first join to be performed is EMPLOYEES JOIN DEPARTMENTS. The first join
condition can reference columns in EMPLOYEES and DEPARTMENTS but cannot reference columns
in LOCATIONS. The second join condition can reference columns from all three tables.
Note: The code example in the slide can also be accomplished with the USING clause:
SELECT e.employee_id, l.city, d.department_name
FROM employees e
JOIN departments d
USING (department_id)
JOIN locations l
USING (location_id)
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Oracle Database 11g: SQL Fundamentals I 6 - 17
Applying Additional Conditions
to a Join
Use the AND clause or the WHERE clause to apply additional
conditions:
SELECT e.employee_id, e.last_name, e.department_id,
d.department_id, d.location_id
FROM
employees e JOIN departments d
ON
(e.department_id = d.department_id)
AND
e.manager_id = 149 ;
Or
SELECT e.employee_id, e.last_name, e.department_id,
d.department_id, d.location_id
FROM
employees e JOIN departments d
ON
(e.department_id = d.department_id)
WHERE
e.manager_id = 149 ;
Copyright © 2009, Oracle. All rights reserved.
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Applying Additional Conditions to a Join
You can apply additional conditions to the join.
The example shown performs a join on the EMPLOYEES and DEPARTMENTS tables and, in
addition, displays only employees who have a manager ID of 149. To add additional conditions to
the ON clause, you can add AND clauses. Alternatively, you can use a WHERE clause to apply
additional conditions.
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Oracle Database 11g: SQL Fundamentals I 6 - 18
Lesson Agenda
•
Types of JOINS and its syntax
•
Natural join:
– USING clause
– ON clause
•
•
•
Self-join
Nonequijoins
OUTER join:
– LEFT OUTER join
– RIGHT OUTER join
– FULL OUTER join
•
Cartesian product
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– Cross join
Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 6 - 19
Joining a Table to Itself
EMPLOYEES (WORKER)
…
EMPLOYEES (MANAGER)
…
MANAGER_ID in the WORKER table is equal to
EMPLOYEE_ID in the MANAGER table.
Copyright © 2009, Oracle. All rights reserved.
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Joining a Table to Itself
Sometimes you need to join a table to itself. To find the name of each employee’s manager, you need
to join the EMPLOYEES table to itself, or perform a self-join. For example, to find the name of
Lorentz’s manager, you need to:
• Find Lorentz in the EMPLOYEES table by looking at the LAST_NAME column
• Find the manager number for Lorentz by looking at the MANAGER_ID column. Lorentz’s
manager number is 103.
• Find the name of the manager with EMPLOYEE_ID 103 by looking at the LAST_NAME column.
Hunold’s employee number is 103, so Hunold is Lorentz’s manager.
In this process, you look in the table twice. The first time you look in the table to find Lorentz in the
LAST_NAME column and the MANAGER_ID value of 103. The second time you look in the
EMPLOYEE_ID column to find 103 and the LAST_NAME column to find Hunold.
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Oracle Database 11g: SQL Fundamentals I 6 - 20
Self-Joins Using the ON Clause
SELECT worker.last_name emp, manager.last_name mgr
FROM
employees worker JOIN employees manager
ON
(worker.manager_id = manager.employee_id);
…
Copyright © 2009, Oracle. All rights reserved.
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Self-Joins Using the ON Clause
The ON clause can also be used to join columns that have different names, within the same table or in
a different table.
The example shown is a self-join of the EMPLOYEES table, based on the EMPLOYEE_ID and
MANAGER_ID columns.
Note: The parenthesis around the joined columns as in the slide example, (e.manager_id =
m.employee_id) is optional. So, even ON e.manager_id = m.employee_id will work.
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Oracle Database 11g: SQL Fundamentals I 6 - 21
Lesson Agenda
•
Types of JOINS and its syntax
•
Natural join:
– USING clause
– ON clause
•
•
•
Self-join
Nonequijoins
OUTER join:
– LEFT OUTER join
– RIGHT OUTER join
– FULL OUTER join
•
Cartesian product
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– Cross join
Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 6 - 22
Nonequijoins
EMPLOYEES
…
JOB_GRADES
JOB_GRADES table defines the
LOWEST_SAL and HIGHEST_SAL range
of values for each GRADE_LEVEL.
Hence, the GRADE_LEVEL column can
be used to assign grades to each
employee.
Copyright © 2009, Oracle. All rights reserved.
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Nonequijoins
A nonequijoin is a join condition containing something other than an equality operator.
The relationship between the EMPLOYEES table and the JOB_GRADES table is an example of a
nonequijoin. The SALARY column in the EMPLOYEES table ranges between the values in the
LOWEST_SAL and HIGHEST_SAL columns of the JOB_GRADES table. Therefore, each employee
can be graded based on their salary. The relationship is obtained using an operator other than the
equality (=) operator.
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Oracle Database 11g: SQL Fundamentals I 6 - 23
Retrieving Records
with Nonequijoins
SELECT e.last_name, e.salary, j.grade_level
FROM
employees e JOIN job_grades j
ON
e.salary
BETWEEN j.lowest_sal AND j.highest_sal;
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Retrieving Records with Nonequijoins
The slide example creates a nonequijoin to evaluate an employee’s salary grade. The salary must be
between any pair of the low and high salary ranges.
It is important to note that all employees appear exactly once when this query is executed. No
employee is repeated in the list. There are two reasons for this:
• None of the rows in the JOB_GRADES table contain grades that overlap. That is, the salary
value for an employee can lie only between the low salary and high salary values of one of the
rows in the salary grade table.
• All of the employees’ salaries lie within the limits provided by the job grade table. That is, no
employee earns less than the lowest value contained in the LOWEST_SAL column or more than
the highest value contained in the HIGHEST_SAL column.
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Note: Other conditions (such as <= and >=) can be used, but BETWEEN is the simplest. Remember
to specify the low value first and the high value last when using the BETWEEN condition. The Oracle
server translates the BETWEEN condition to a pair of AND conditions. Therefore, using BETWEEN has
no performance benefits, but should be used only for logical simplicity.
Table aliases have been specified in the slide example for performance reasons, not because of
possible ambiguity.
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Oracle Database 11g: SQL Fundamentals I 6 - 24
Lesson Agenda
•
Types of JOINS and its syntax
•
Natural join:
– USING clause
– ON clause
•
•
•
Self-join
Nonequijoins
uijo
OUTER join:
– LEFT OUTER join
– RIGHT OUTER join
– FULL OUTER join
•
Cartesian product
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– Cross join
Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 6 - 25
Returning Records with No Direct Match
Using OUTER Joins
DEPARTMENTS
There are no employees
in department 190.
Equijoin with EMPLOYEES
…
Employee “Grant” has
not been assigned a
department ID.
Copyright © 2009, Oracle. All rights reserved.
Returning Records with No Direct Match Using OUTER Joins
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If a row does not satisfy a join condition, the row does not appear in the query result.
In the slide example, a simple equijoin condition is used on the EMPLOYEES and DEPARTMENTS
tables to return the result on the right. The result set does not contain the following:
• Department ID 190, because there are no employees with that department ID recorded in the
EMPLOYEES table
• The employee with the last name of Grant, because this employee has not been assigned a
department ID
To return the department record that does not have any employees, or employees that do not have an
assigned department, you can use an OUTER join.
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Oracle Database 11g: SQL Fundamentals I 6 - 26
INNER Versus OUTER Joins
•
In SQL:1999, the join of two tables returning only matched
rows is called an INNER join.
•
A join between two tables that returns the results of the
INNER join as well as the unmatched rows from the left (or
right) table is called a left (or right) OUTER join.
•
A join between two tables that returns the results of an
INNER join as well as the results of a left and right join is a
full OUTER join.
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INNER Versus OUTER Joins
Joining tables with the NATURAL JOIN, USING, or ON clauses results in an INNER join. Any
unmatched rows are not displayed in the output. To return the unmatched rows, you can use an
OUTER join. An OUTER join returns all rows that satisfy the join condition and also returns some or
all of those rows from one table for which no rows from the other table satisfy the join condition.
There are three types of OUTER joins:
• LEFT OUTER
• RIGHT OUTER
• FULL OUTER
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Oracle Database 11g: SQL Fundamentals I 6 - 27
LEFT OUTER JOIN
SELECT e.last_name, e.department_id, d.department_name
FROM
employees e LEFT OUTER JOIN departments d
ON
(e.department_id = d.department_id) ;
…
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LEFT OUTER JOIN
This query retrieves all the rows in the EMPLOYEES table, which is the left table, even if there is no
match in the DEPARTMENTS table.
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Oracle Database 11g: SQL Fundamentals I 6 - 28
RIGHT OUTER JOIN
SELECT e.last_name, d.department_id, d.department_name
FROM
employees e RIGHT OUTER JOIN departments d
ON
(e.department_id = d.department_id) ;
…
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RIGHT OUTER JOIN
This query retrieves all the rows in the DEPARTMENTS table, which is the table at the right, even if
there is no match in the EMPLOYEES table.
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Oracle Database 11g: SQL Fundamentals I 6 - 29
FULL OUTER JOIN
SELECT e.last_name, d.department_id, d.department_name
FROM
employees e FULL OUTER JOIN departments d
ON
(e.department_id = d.department_id) ;
…
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Copyright © 2009, Oracle. All rights reserved.
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FULL OUTER JOIN
This query retrieves all rows in the EMPLOYEES table, even if there is no match in the
DEPARTMENTS table. It also retrieves all rows in the DEPARTMENTS table, even if there is no
match in the EMPLOYEES table.
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Oracle Database 11g: SQL Fundamentals I 6 - 30
Lesson Agenda
•
Types of JOINS and its syntax
•
Natural join:
– USING clause
– ON clause
•
•
•
Self-join
Nonequiijoin
OUTER join:
– LEFT OUTER join
– RIGHT OUTER join
– FULL OUTER join
•
Cartesian product
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– Cross join
Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 6 - 31
Cartesian Products
•
A Cartesian product is formed when:
– A join condition is omitted
– A join condition is invalid
– All rows in the first table are joined to all rows in the second
table
•
To avoid a Cartesian product, always include a valid join
condition.
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Cartesian Products
When a join condition is invalid or omitted completely, the result is a Cartesian product, in which all
combinations of rows are displayed. All rows in the first table are joined to all rows in the second
table.
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A Cartesian product tends to generate a large number of rows and the result is rarely useful. You
should, therefore, always include a valid join condition unless you have a specific need to combine
all rows from all tables.
However, Cartesian products are useful for some tests when you need to generate a large number of
rows to simulate a reasonable amount of data.
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Oracle Database 11g: SQL Fundamentals I 6 - 32
Generating a Cartesian Product
EMPLOYEES (20 rows)
DEPARTMENTS (8 rows)
…
Cartesian product:
20 x 8 = 160 rows
…
Copyright © 2009, Oracle. All rights reserved.
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Generating a Cartesian Product
A Cartesian product is generated if a join condition is omitted. The example in the slide displays the
employee last name and the department name from the EMPLOYEES and DEPARTMENTS tables.
Because no join condition was specified, all rows (20 rows) from the EMPLOYEES table are joined
with all rows (8 rows) in the DEPARTMENTS table, thereby generating 160 rows in the output.
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Oracle Database 11g: SQL Fundamentals I 6 - 33
Creating Cross Joins
•
The CROSS JOIN clause produces the cross-product of
two tables.
This is also called a Cartesian product between the two
tables.
•
SELECT last_name, department_name
FROM
employees
CROSS JOIN departments ;
…
Copyright © 2009, Oracle. All rights reserved.
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Creating Cross Joins
The example in the slide produces a Cartesian product of the EMPLOYEES and DEPARTMENTS
tables.
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Oracle Database 11g: SQL Fundamentals I 6 - 34
Quiz
The SQL:1999 standard join syntax supports the following
types of joins. Which of these join types does Oracle join syntax
support?
1. Equijoins
2. Nonequijoins
3. Left OUTER join
4. Right OUTER join
5. Full OUTER join
6. Self joins
7. Natural joins
8. Cartesian products
Copyright © 2009, Oracle. All rights reserved.
Answer: 1, 2, 3, 4, 6, 8
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Oracle Database 11g: SQL Fundamentals I 6 - 35
Summary
In this lesson, you should have learned how to use joins to
display data from multiple tables by using:
• Equijoins
• Nonequijoins
• OUTER joins
•
•
•
•
Self-joins
Cross joins
Natural joins
Full (or two-sided) OUTER joins
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Copyright © 2009, Oracle. All rights reserved.
Summary
There are multiple ways to join tables.
Types of Joins
• Equijoins
• Nonequijoins
• OUTER joins
• Self-joins
• Cross joins
• Natural joins
• Full (or two-sided) OUTER joins
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Cartesian Products
A Cartesian product results in the display of all combinations of rows. This is done by either omitting
the WHERE clause or by specifying the CROSS JOIN clause.
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Table Aliases
• Table aliases speed up database access.
• Table aliases can help to keep SQL code smaller by conserving memory.
• Table aliases are sometimes mandatory to avoid column ambiguity.
Oracle Database 11g: SQL Fundamentals I 6 - 36
Practice 6: Overview
This practice covers the following topics:
• Joining tables using an equijoin
• Performing outer and self-joins
• Adding conditions
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Practice 6: Overview
This practice is intended to give you experience in extracting data from more than one table using the
SQL:1999–compliant joins.
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Oracle Database 11g: SQL Fundamentals I 6 - 37
Practice 6
1. Write a query for the HR department to produce the addresses of all the departments. Use the
LOCATIONS and COUNTRIES tables. Show the location ID, street address, city, state or
province, and country in the output. Use a NATURAL JOIN to produce the results.
2. The HR department needs a report of all employees. Write a query to display the last name,
department number, and department name for all the employees.
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Oracle Database 11g: SQL Fundamentals I 6 - 38
Practice 6 (continued)
3. The HR department needs a report of employees in Toronto. Display the last name, job,
department number, and the department name for all employees who work in Toronto.
4. Create a report to display employees’ last name and employee number along with their
manager’s last name and manager number. Label the columns Employee, Emp#, Manager,
and Mgr#, respectively. Save your SQL statement as lab_06_04.sql. Run the query.
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Oracle Database 11g: SQL Fundamentals I 6 - 39
Practice 6 (continued)
5. Modify lab_06_04.sql to display all employees including King, who has no manager.
Order the results by the employee number. Save your SQL statement as lab_06_05.sql.
Run the query in lab_06_05.sql.
…
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6. Create a report for the HR department that displays employee last names, department numbers,
and all the employees who work in the same department as a given employee. Give each
column an appropriate label. Save the script to a file named lab_06_06.sql.
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Oracle Database 11g: SQL Fundamentals I 6 - 40
Practice 6 (continued)
7. The HR department needs a report on job grades and salaries. To familiarize yourself with the
JOB_GRADES table, first show the structure of the JOB_GRADES table. Then create a query
that displays the name, job, department name, salary, and grade for all employees.
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Oracle Database 11g: SQL Fundamentals I 6 - 41
Practice 6 (continued)
If you want an extra challenge, complete the following exercises:
8. The HR department wants to determine the names of all the employees who were hired after
Davies. Create a query to display the name and hire date of any employee hired after employee
Davies.
9. The HR department needs to find the names and hire dates of all the employees who were hired
before their managers, along with their managers’ names and hire dates. Save the script to a file
named lab_06_09.sql.
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Oracle Database 11g: SQL Fundamentals I 6 - 42
Using Subqueries to Solve Queries
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Objectives
After completing this lesson, you should be able to do the
following:
• Define subqueries
• Describe the types of problems that the subqueries can
solve
• List the types of subqueries
• Write single-row and multiple-row subqueries
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Objectives
In this lesson, you learn about the more advanced features of the SELECT statement. You can write
subqueries in the WHERE clause of another SQL statement to obtain values based on an unknown
conditional value. This lesson also covers single-row subqueries and multiple-row subqueries.
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Oracle Database 11g: SQL Fundamentals I 7 - 2
Lesson Agenda
•
•
Subquery: Types, syntax, and guidelines
Single-row subqueries:
– Group functions in a subquery
– HAVING clause with subqueries
•
Multiple-row subqueries
– Use ALL or ANY operator.
•
Null values in a subquery
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Oracle Database 11g: SQL Fundamentals I 7 - 3
Using a Subquery to Solve a Problem
Who has a salary greater than Abel’s?
Main query:
Which employees have salaries greater than Abel’s
salary?
Subquery:
What is Abel’s salary?
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Using a Subquery to Solve a Problem
Suppose you want to write a query to find out who earns a salary greater than Abel’s salary.
To solve this problem, you need two queries: one to find how much Abel earns, and a second query
to find who earns more than that amount.
You can solve this problem by combining the two queries, placing one query inside the other query.
The inner query (or subquery) returns a value that is used by the outer query (or main query). Using a
subquery is equivalent to performing two sequential queries and using the result of the first query as
the search value in the second query.
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Oracle Database 11g: SQL Fundamentals I 7 - 4
Subquery Syntax
SELECT
FROM
WHERE
•
select_list
table
expr operator
(SELECT
FROM
select_list
table);
•
The subquery (inner query) executes before the main
query (outer query).
The result of the subquery is used by the main query.
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Subquery Syntax
A subquery is a SELECT statement that is embedded in the clause of another SELECT statement.
You can build powerful statements out of simple ones by using subqueries. They can be very useful
when you need to select rows from a table with a condition that depends on the data in the table
itself.
You can place the subquery in a number of SQL clauses, including the following:
• WHERE clause
• HAVING clause
• FROM clause
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In the syntax:
operator includes a comparison condition such as >, =, or IN
Note: Comparison conditions fall into two classes: single-row operators (>, =, >=, <, <>, <=) and
multiple-row operators (IN, ANY, ALL).
The subquery is often referred to as a nested SELECT, sub-SELECT, or inner SELECT statement.
The subquery generally executes first, and its output is used to complete the query condition for the
main (or outer) query.
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Oracle Database 11g: SQL Fundamentals I 7 - 5
Using a Subquery
SELECT last_name, salary
FROM
employees
11000
WHERE salary >
(SELECT salary
FROM
employees
WHERE last_name = 'Abel');
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Using a Subquery
In the slide, the inner query determines the salary of employee Abel. The outer query takes the result
of the inner query and uses this result to display all the employees who earn more than employee
Abel.
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Oracle Database 11g: SQL Fundamentals I 7 - 6
Guidelines for Using Subqueries
•
•
•
Enclose subqueries in parentheses.
Place subqueries on the right side of the comparison
condition for readability (However, the subquery can
appear on either side of the comparison operator.).
Use single-row operators with single-row subqueries and
multiple-row operators with multiple-row subqueries.
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Guidelines for Using Subqueries
• A subquery must be enclosed in parentheses.
• Place the subquery on the right side of the comparison condition for readability. However, the
subquery can appear on either side of the comparison operator.
• Two classes of comparison conditions are used in subqueries: single-row operators and
multiple-row operators.
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Oracle Database 11g: SQL Fundamentals I 7 - 7
Types of Subqueries
•
Single-row subquery
Main query
Subquery
•
returns
ST_CLERK
Multiple-row subquery
Main query
Subquery
returns
ST_CLERK
SA_MAN
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Types of Subqueries
• Single-row subqueries: Queries that return only one row from the inner SELECT statement
• Multiple-row subqueries: Queries that return more than one row from the inner SELECT
statement
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Note: There are also multiple-column subqueries, which are queries that return more than one
column from the inner SELECT statement. These are covered in the Oracle Database 11g: SQL
Fundamentals II course.
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Oracle Database 11g: SQL Fundamentals I 7 - 8
Lesson Agenda
•
•
Subquery: Types, syntax, and guidelines
Single-row subqueries:
– Group functions in a subquery
– HAVING clause with subqueries
•
Multiple-row subqueries
– Use ALL or ANY operator
•
Null values in a subquery
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Oracle Database 11g: SQL Fundamentals I 7 - 9
Single-Row Subqueries
•
•
Return only one row
Use single-row comparison operators
Operator
=
Meaning
Equal to
>
Greater than
>=
Greater than or equal to
<
Less than
<=
Less than or equal to
<>
Not equal to
Copyright © 2009, Oracle. All rights reserved.
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Single-Row Subqueries
A single-row subquery is one that returns one row from the inner SELECT statement. This type of
subquery uses a single-row operator. The slide gives a list of single-row operators.
Example:
Display the employees whose job ID is the same as that of employee 141:
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SELECT last_name, job_id
FROM
employees
WHERE job_id =
(SELECT job_id
FROM
employees
WHERE employee_id = 141);
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Oracle Database 11g: SQL Fundamentals I 7 - 10
Executing Single-Row Subqueries
SELECT last_name, job_id, salary
FROM
employees
SA_REP
WHERE job_id =
(SELECT job_id
FROM
employees
WHERE last_name = ‘Taylor’)
AND
salary >
8600
(SELECT salary
FROM
employees
WHERE last_name = ‘Taylor’);
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Executing Single-Row Subqueries
A SELECT statement can be considered as a query block. The example in the slide displays
employees who do the same job as “Taylor,” but earn more salary than him.
The example consists of three query blocks: the outer query and two inner queries. The inner query
blocks are executed first, producing the query results SA_REP and 8600, respectively. The outer
query block is then processed and uses the values that were returned by the inner queries to complete
its search conditions.
Both inner queries return single values (SA_REP and 8600, respectively), so this SQL statement is
called a single-row subquery.
Note: The outer and inner queries can get data from different tables.
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Oracle Database 11g: SQL Fundamentals I 7 - 11
Using Group Functions in a Subquery
SELECT last_name, job_id, salary
FROM
employees
2500
WHERE salary =
(SELECT MIN(salary)
FROM
employees);
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Using Group Functions in a Subquery
You can display data from a main query by using a group function in a subquery to return a single
row. The subquery is in parentheses and is placed after the comparison condition.
The example in the slide displays the employee last name, job ID, and salary of all employees whose
salary is equal to the minimum salary. The MIN group function returns a single value (2500) to the
outer query.
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Oracle Database 11g: SQL Fundamentals I 7 - 12
The HAVING Clause with Subqueries
•
•
The Oracle server executes the subqueries first.
The Oracle server returns results into the HAVING clause
of the main query.
SELECT
FROM
GROUP BY
HAVING
department_id, MIN(salary)
employees
department_id
2500
MIN(salary) >
(SELECT MIN(salary)
FROM
employees
WHERE department_id = 50);
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The HAVING Clause with Subqueries
You can use subqueries not only in the WHERE clause, but also in the HAVING clause. The Oracle
server executes the subquery and the results are returned into the HAVING clause of the main query.
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The SQL statement in the slide displays all the departments that have a minimum salary greater than
that of department 50.
Example:
Find the job with the lowest average salary.
SELECT
FROM
GROUP BY
HAVING
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job_id, AVG(salary)
employees
job_id
AVG(salary) = (SELECT
MIN(AVG(salary))
FROM
employees
GROUP BY job_id);
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Oracle Database 11g: SQL Fundamentals I 7 - 13
What Is Wrong with This Statement?
SELECT employee_id, last_name
FROM
employees
WHERE salary =
(SELECT
MIN(salary)
FROM
employees
GROUP BY department_id);
Single-row operator
with multiple-row
subquery
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What Is Wrong with This Statement?
A common error with subqueries occurs when more than one row is returned for a single-row
subquery.
In the SQL statement in the slide, the subquery contains a GROUP BY clause, which implies that the
subquery will return multiple rows, one for each group that it finds. In this case, the results of the
subquery are 4400, 6000, 2500, 4200, 7000, 17000, and 8300.
The outer query takes those results and uses them in its WHERE clause. The WHERE clause contains
an equal (=) operator, a single-row comparison operator that expects only one value. The = operator
cannot accept more than one value from the subquery and, therefore, generates the error.
To correct this error, change the = operator to IN.
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Oracle Database 11g: SQL Fundamentals I 7 - 14
No Rows Returned by the Inner Query
SELECT last_name, job_id
FROM
employees
WHERE job_id =
(SELECT job_id
FROM
employees
WHERE last_name = 'Haas');
Subquery returns no rows because there is no
employee named “Haas.”
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No Rows Returned by the Inner Query
A common problem with subqueries occurs when no rows are returned by the inner query.
In the SQL statement in the slide, the subquery contains a WHERE clause. Presumably, the intention
is to find the employee whose name is Haas. The statement is correct, but selects no rows when
executed.
Because, there is no employee named Haas. So the subquery returns no rows. The outer query takes
the results of the subquery (null) and uses these results in its WHERE clause. The outer query finds no
employee with a job ID equal to null, and so returns no rows. If a job existed with a value of null, the
row is not returned because comparison of two null values yields a null; therefore, the WHERE
condition is not true.
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Oracle Database 11g: SQL Fundamentals I 7 - 15
Lesson Agenda
•
•
Subquery: Types, syntax, and guidelines
Single-row subqueries:
– Group functions in a subquery
– HAVING clause with subqueries
•
Multiple-row subqueries
– Use ALL or ANY operator
•
Null values in a subquery
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Oracle Database 11g: SQL Fundamentals I 7 - 16
Multiple-Row Subqueries
•
•
Return more than one row
Use multiple-row comparison operators
Operator
Meaning
IN
Equal to any member in the list
ANY
Must be preceded by =, !=, >, <, <=, >=.
Compares a value to each value in a list or
returned by a query. Evaluates to FALSE if the
query returns no rows.
ALL
Must be preceded by =, !=, >, <, <=, >=.
Compares a value to every value in a list or
returned by a query. Evaluates to TRUE if the
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query returns no rows.
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Multiple-Row Subqueries
Subqueries that return more than one row are called multiple-row subqueries. You use a multiple-row
operator, instead of a single-row operator, with a multiple-row subquery. The multiple-row operator
expects one or more values:
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SELECT last_name, salary, department_id
FROM
employees
WHERE salary IN (SELECT
MIN(salary)
FROM
employees
GROUP BY department_id);
Example:
Find the employees who earn the same salary as the minimum salary for each department.
The inner query is executed first, producing a query result. The main query block is then processed
and uses the values that were returned by the inner query to complete its search condition. In fact, the
main query appears to the Oracle server as follows:
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SELECT
FROM
WHERE
8600,
last_name, salary, department_id
employees
salary IN (2500, 4200, 4400, 6000, 7000, 8300,
17000);
Oracle Database 11g: SQL Fundamentals I 7 - 17
Using the ANY Operator
in Multiple-Row Subqueries
SELECT employee_id, last_name, job_id, salary
FROM
employees
9000, 6000, 4200
WHERE salary < ANY
(SELECT salary
FROM
employees
WHERE job_id = 'IT_PROG')
AND
job_id <> 'IT_PROG';
…
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Using the ANY Operator in Multiple-Row Subqueries
The ANY operator (and its synonym, the SOME operator) compares a value to each value returned by
a subquery. The slide example displays employees who are not IT programmers and whose salary is
less than that of any IT programmer. The maximum salary that a programmer earns is $9,000.
ANY means more than the minimum. =ANY is equivalent to
IN.
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Oracle Database 11g: SQL Fundamentals I 7 - 18
Using the ALL Operator
in Multiple-Row Subqueries
SELECT employee_id, last_name, job_id, salary
FROM
employees
9000, 6000, 4200
WHERE salary < ALL
(SELECT salary
FROM
employees
WHERE job_id = 'IT_PROG')
AND
job_id <> 'IT_PROG';
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Using the ALL Operator in Multiple-Row Subqueries
The ALL operator compares a value to every value returned by a subquery. The example in the slide
displays employees whose salary is less than the salary of all employees with a job ID of IT_PROG
and whose job is not IT_PROG.
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>ALL means more than the maximum and ALL.
Notice that the null value as part of the results set of a subquery is not a problem if you use the IN
operator. The IN operator is equivalent to =ANY. For example, to display the employees who have
subordinates, use the following SQL statement:
SELECT emp.last_name
FROM
employees emp
WHERE emp.employee_id
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IN
(SELECT mgr.manager_id
FROM
employees mgr);
Oracle Database 11g: SQL Fundamentals I 7 - 21
Null Values in a Subquery (continued)
Alternatively, a WHERE clause can be included in the subquery to display all employees who do not
have any subordinates:
SELECT last_name FROM employees
WHERE employee_id NOT IN
(SELECT manager_id
FROM
employees
WHERE manager_id IS NOT NULL);
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Oracle Database 11g: SQL Fundamentals I 7 - 22
Quiz
Using a subquery is equivalent to performing two sequential
queries and using the result of the first query as the search
value(s) in the second query.
1. True
2. False
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Copyright © 2009, Oracle. All rights reserved.
Answer: 1
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Oracle Database 11g: SQL Fundamentals I 7 - 23
Summary
In this lesson, you should have learned how to:
• Identify when a subquery can help solve a problem
• Write subqueries when a query is based on unknown
values
SELECT
FROM
WHERE
select_list
table
expr operator
(SELECT select_list
FROM
table);
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Summary
In this lesson, you should have learned how to use subqueries. A subquery is a SELECT statement
that is embedded in the clause of another SQL statement. Subqueries are useful when a query is
based on a search criterion with unknown intermediate values.
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Subqueries have the following characteristics:
• Can pass one row of data to a main statement that contains a single-row operator, such as =, <>,
>, >=, <, or <=
• Can pass multiple rows of data to a main statement that contains a multiple-row operator, such
as IN
• Are processed first by the Oracle server, after which the WHERE or HAVING clause uses the
results
• Can contain group functions
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Oracle Database 11g: SQL Fundamentals I 7 - 24
Practice 7: Overview
This practice covers the following topics:
• Creating subqueries to query values based on unknown
criteria
• Using subqueries to find out the values that exist in one set
of data and not in another
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Practice 7: Overview
In this practice, you write complex queries using nested SELECT statements.
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For practice questions, you may want to create the inner query first. Make sure that it runs and
produces the data that you anticipate before you code the outer query.
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Oracle Database 11g: SQL Fundamentals I 7 - 25
Practice 7
1. The HR department needs a query that prompts the user for an employee last name. The query
then displays the last name and hire date of any employee in the same department as the
employee whose name they supply (excluding that employee). For example, if the user enters
Zlotkey, find all employees who work with Zlotkey (excluding Zlotkey).
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2. Create a report that displays the employee number, last name, and salary of all employees who
earn more than the average salary. Sort the results in order of ascending salary.
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Oracle Database 11g: SQL Fundamentals I 7 - 26
Practice 7 (continued)
3. Write a query that displays the employee number and last name of all employees who work in a
department with any employee whose last name contains the letter “u.” Save your SQL
statement as lab_07_03.sql. Run your query.
4. The HR department needs a report that displays the last name, department number, and job ID
of all employees whose department location ID is 1700.
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Modify the query so that the user is prompted for a location ID. Save this to a file named
lab_07_04.sql.
5. Create a report for HR that displays the last name and salary of every employee who reports to
King.
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Oracle Database 11g: SQL Fundamentals I 7 - 27
Practice 7 (continued)
6. Create a report for HR that displays the department number, last name, and job ID for every
employee in the Executive department.
If you have the time, complete the following exercise:
7. Modify the query in lab_07_03.sql to display the employee number, last name, and salary
of all employees who earn more than the average salary, and who work in a department with
any employee whose last name contains a “u.” Resave lab_07_03.sql as
lab_07_07.sql. Run the statement in lab_07_07.sql.
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Oracle Database 11g: SQL Fundamentals I 7 - 28
Using the Set Operators
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Objectives
After completing this lesson, you should be able to do the
following:
• Describe set operators
• Use a set operator to combine multiple queries into a
single query
• Control the order of rows returned
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Copyright © 2009, Oracle. All rights reserved.
Objectives
In this lesson, you learn how to write queries by using set operators.
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Oracle Database 11g: SQL Fundamentals I 8 - 2
Lesson Agenda
•
•
•
•
•
•
•
Set Operators: Types and guidelines
Tables used in this lesson
UNION and UNION ALL operator
INTERSECT operator
MINUS operator
Matching the SELECT statements
Using the ORDER BY clause in set operations
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Oracle Database 11g: SQL Fundamentals I 8 - 3
Set Operators
A
B
A
B
UNION/UNION ALL
A
B
INTERSECT
A
B
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MINUS
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Set Operators
Set operators combine the results of two or more component queries into one result. Queries
containing set operators are called compound queries.
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Operator
Returns
UNION
Rows from both queries after eliminating duplications
UNION ALL
Rows from both queries, including all duplications
INTERSECT
Rows that are common to both queries
MINUS
Rows in the first query that are not present in the second query
All set operators have equal precedence. If a SQL statement contains multiple set operators, the
Oracle server evaluates them from left (top) to right (bottom)—if no parentheses explicitly specify
another order. You should use parentheses to specify the order of evaluation explicitly in queries that
use the INTERSECT operator with other set operators.
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Oracle Database 11g: SQL Fundamentals I 8 - 4
Set Operator Guidelines
•
•
The expressions in the SELECT lists must match in
number.
The data type of each column in the second query must
match the data type of its corresponding column in the first
query.
Parentheses can be used to alter the sequence of
execution.
ORDER BY clause can appear only at the very end of the
statement.
•
•
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Set Operator Guidelines
• The expressions in the SELECT lists of the queries must match in number and data type. Queries
that use UNION, UNION ALL, INTERSECT, and MINUS operators in their WHERE clause must
have the same number and data type of columns in their SELECT list. The data type of the
columns in SELECT list of the queries in the compound query may not be exactly the same. The
column in second query must be in the same data type group (such as numeric or character) as
the corresponding column in the first query.
• Set operators can be used in subqueries.
• You should use parentheses to specify the order of evaluation in queries that use the
INTERSECT operator with other set operators. This ensures compliance with emerging SQL
standards that will give the INTERSECT operator greater precedence than the other set
operators.
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Oracle Database 11g: SQL Fundamentals I 8 - 5
The Oracle Server and Set Operators
•
Duplicate rows are automatically eliminated except in
UNION ALL.
•
•
Column names from the first query appear in the result.
The output is sorted in ascending order by default except
in UNION ALL.
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The Oracle Server and Set Operators
When a query uses set operators, the Oracle server eliminates duplicate rows automatically except in
the case of the UNION ALL operator. The column names in the output are decided by the column list
in the first SELECT statement. By default, the output is sorted in ascending order of the first column
of the SELECT clause.
The corresponding expressions in the SELECT lists of the component queries of a compound query
must match in number and data type. If component queries select character data, the data type of the
return values is determined as follows:
• If both queries select values of CHAR data type, of equal length, then the returned values have
the CHAR data type of that length. If the queries select values of CHAR with different lengths,
then the returned value is VARCHAR2 with the length of the larger CHAR value.
• If either or both of the queries select values of VARCHAR2 data type, then the returned values
have the VARCHAR2 data type.
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If component queries select numeric data, then the data type of the return values is determined by
numeric precedence. If all queries select values of the NUMBER type, then the returned values have
the NUMBER data type. In queries using set operators, the Oracle server does not perform implicit
conversion across data type groups. Therefore, if the corresponding expressions of component
queries resolve to both character data and numeric data, the Oracle server returns an error.
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Oracle Database 11g: SQL Fundamentals I 8 - 6
Lesson Agenda
•
•
•
•
•
•
•
Set Operators: Types and guidelines
Tables used in this lesson
UNION and UNION ALL operator
INTERSECT operator
MINUS operator
Matching the SELECT statements
Using the ORDER BY clause in set operations
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 8 - 7
Tables Used in This Lesson
The tables used in this lesson are:
• EMPLOYEES: Provides details regarding all current
employees
• JOB_HISTORY: Records the details of the start date and
end date of the former job, and the job identification
number and department when an employee switches jobs
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Copyright © 2009, Oracle. All rights reserved.
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Tables Used in This Lesson
Two tables are used in this lesson. They are the EMPLOYEES table and the JOB_HISTORY table.
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You are already familiar with the EMPLOYEES table that stores employee details such as a unique
identification number, email address, job identification (such as ST_CLERK, SA_REP, and so on),
salary, manager and so on.
Some of the employees have been with the company for a long time and have switched to different
jobs. This is monitored using the JOB_HISTORY table. When an employee switches jobs, the details
of the start date and end date of the former job, the job_id (such as ST_CLERK, SA_REP, and so
on), and the department are recorded in the JOB_HISTORY table.
The structure and data from the EMPLOYEES and JOB_HISTORY tables are shown on the following
pages.
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Oracle Database 11g: SQL Fundamentals I 8 - 8
Tables Used in This Lesson (continued)
There have been instances in the company, of people who have held the same position more than
once during their tenure with the company. For example, consider the employee Taylor, who joined
the company on 24-MAR-1998. Taylor held the job title SA_REP for the period 24-MAR-98 to 31DEC-98 and the job title SA_MAN for the period 01-JAN-99 to 31-DEC-99. Taylor moved back into
the job title of SA_REP, which is his current job title.
DESCRIBE employees
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Oracle Database 11g: SQL Fundamentals I 8 - 9
Tables Used in This Lesson (continued)
SELECT employee_id, last_name, job_id, hire_date, department_id
FROM employees;
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DESCRIBE job_history
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Oracle Database 11g: SQL Fundamentals I 8 - 10
Tables Used in This Lesson (continued)
SELECT * FROM job_history;
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Oracle Database 11g: SQL Fundamentals I 8 - 11
Lesson Agenda
•
•
•
•
•
•
•
Set Operators: Types and guidelines
Tables used in this lesson
UNION and UNION ALL operator
INTERSECT operator
MINUS operator
Matching the SELECT statements
Using the ORDER BY clause in set operations
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 8 - 12
UNION Operator
A
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The UNION operator returns rows from both queries after eliminating
duplications.
Copyright © 2009, Oracle. All rights reserved.
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UNION Operator
The UNION operator returns all rows that are selected by either query. Use the UNION operator to
return all rows from multiple tables and eliminate any duplicate rows.
Guidelines
• The number of columns being selected must be the same.
• The data types of the columns being selected must be in the same data type group (such as
numeric or character).
• The names of the columns need not be identical.
• UNION operates over all of the columns being selected.
• NULL values are not ignored during duplicate checking.
• By default, the output is sorted in ascending order of the columns of the SELECT clause.
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Oracle Database 11g: SQL Fundamentals I 8 - 13
Using the UNION Operator
Display the current and previous job details of all employees.
Display each employee only once.
SELECT
FROM
UNION
SELECT
FROM
employee_id, job_id
employees
employee_id, job_id
job_history;
…
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…
Copyright © 2009, Oracle. All rights reserved.
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Using the UNION Operator
The UNION operator eliminates any duplicate records. If records that occur in both the EMPLOYEES
and the JOB_HISTORY tables are identical, the records are displayed only once. Observe in the
output shown in the slide that the record for the employee with the EMPLOYEE_ID 200 appears
twice because the JOB_ID is different in each row.
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Consider the following example:
SELECT
FROM
UNION
SELECT
FROM
employee_id, job_id, department_id
employees
employee_id, job_id, department_id
job_history;
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Oracle Database 11g: SQL Fundamentals I 8 - 14
Using the UNION Operator (continued)
In the preceding output, employee 200 appears three times. Why? Note the DEPARTMENT_ID
values for employee 200. One row has a DEPARTMENT_ID of 90, another 10, and the third 90.
Because of these unique combinations of job IDs and department IDs, each row for employee 200 is
unique and therefore not considered to be a duplicate. Observe that the output is sorted in ascending
order of the first column of the SELECT clause (in this case, EMPLOYEE_ID).
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Oracle Database 11g: SQL Fundamentals I 8 - 15
UNION ALL Operator
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The UNION ALL operator returns rows from both queries, including all
duplications.
Copyright © 2009, Oracle. All rights reserved.
UNION ALL Operator
Use the UNION ALL operator to return all rows from multiple queries.
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Guidelines
The guidelines for UNION and UNION ALL are the same, with the following two exceptions that
pertain to UNION ALL: Unlike UNION, duplicate rows are not eliminated and the output is not sorted
by default.
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Oracle Database 11g: SQL Fundamentals I 8 - 16
Using the UNION ALL Operator
Display the current and previous departments of all employees.
SELECT employee_id, job_id, department_id
FROM
employees
UNION ALL
SELECT employee_id, job_id, department_id
FROM
job_history
ORDER BY employee_id;
…
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…
Copyright © 2009, Oracle. All rights reserved.
Using the UNION ALL Operator
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In the example, 30 rows are selected. The combination of the two tables totals to 30 rows. The
UNION ALL operator does not eliminate duplicate rows. UNION returns all distinct rows selected by
either query. UNION ALL returns all rows selected by either query, including all duplicates. Consider
the query in the slide, now written with the UNION clause:
SELECT
FROM
UNION
SELECT
FROM
ORDER BY
employee_id, job_id,department_id
employees
employee_id, job_id,department_id
job_history
employee_id;
The preceding query returns 29 rows. This is because it eliminates the following row (because it is a
duplicate):
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Oracle Database 11g: SQL Fundamentals I 8 - 17
Lesson Agenda
•
•
•
•
•
•
•
Set Operators: Types and guidelines
Tables used in this lesson
UNION and UNION ALL operator
INTERSECT operator
MINUS operator
Matching the SELECT statements
Using ORDER BY clause in set operations
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 8 - 18
INTERSECT Operator
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The INTERSECT operator returns rows that are common to both queries.
Copyright © 2009, Oracle. All rights reserved.
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INTERSECT Operator
Use the INTERSECT operator to return all rows that are common to multiple queries.
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Guidelines
• The number of columns and the data types of the columns being selected by the SELECT
statements in the queries must be identical in all the SELECT statements used in the query. The
names of the columns, however, need not be identical.
• Reversing the order of the intersected tables does not alter the result.
• INTERSECT does not ignore NULL values.
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Oracle Database 11g: SQL Fundamentals I 8 - 19
Using the INTERSECT Operator
Display the employee IDs and job IDs of those employees who
currently have a job title that is the same as their previous one
(that is, they changed jobs but have now gone back to doing
the same job they did previously).
SELECT employee_id, job_id
FROM
employees
INTERSECT
SELECT employee_id, job_id
FROM
job_history;
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Copyright © 2009, Oracle. All rights reserved.
Using the INTERSECT Operator
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In the example in this slide, the query returns only those records that have the same values in the
selected columns in both tables.
What will be the results if you add the DEPARTMENT_ID column to the SELECT statement from
the EMPLOYEES table and add the DEPARTMENT_ID column to the SELECT statement from the
JOB_HISTORY table, and run this query? The results may be different because of the introduction
of another column whose values may or may not be duplicates.
Example:
SELECT employee_id, job_id, department_id
FROM
employees
INTERSECT
SELECT employee_id, job_id, department_id
FROM
job_history;
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Employee 200 is no longer part of the results because the EMPLOYEES.DEPARTMENT_ID value is
different from the JOB_HISTORY.DEPARTMENT_ID value.
Oracle Database 11g: SQL Fundamentals I 8 - 20
Lesson Agenda
•
•
•
•
•
•
•
Set Operators: Types and guidelines
Tables used in this lesson
UNION and UNION ALL operator
INTERSECT operator
MINUS operator
Matching the SELECT statements
Using the ORDER BY clause in set operations
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 8 - 21
MINUS Operator
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The MINUS operator returns all the distinct rows selected by the first
query, but not present in the second query result set.
Copyright © 2009, Oracle. All rights reserved.
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MINUS Operator
Use the MINUS operator to return all distinct rows selected by the first query, but not present in the
second query result set (the first SELECT statement MINUS the second SELECT statement).
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Note: The number of columns must be the same and the data types of the columns being selected by
the SELECT statements in the queries must belong to the same data type group in all the SELECT
statements used in the query. The names of the columns, however, need not be identical.
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Oracle Database 11g: SQL Fundamentals I 8 - 22
Using the MINUS Operator
Display the employee IDs of those employees who have not
changed their jobs even once.
SELECT
FROM
MINUS
SELECT
FROM
employee_id
employees
employee_id
job_history;
…
Copyright © 2009, Oracle. All rights reserved.
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Using the MINUS Operator
In the example in the slide, the employee IDs in the JOB_HISTORY table are subtracted from those
in the EMPLOYEES table. The results set displays the employees remaining after the subtraction;
they are represented by rows that exist in the EMPLOYEES table, but do not exist in the
JOB_HISTORY table. These are the records of the employees who have not changed their jobs even
once.
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Oracle Database 11g: SQL Fundamentals I 8 - 23
Lesson Agenda
•
•
•
•
•
•
•
Set Operators: Types and guidelines
Tables used in this lesson
UNION and UNION ALL operator
INTERSECT operator
MINUS operator
Matching the SELECT statements
Using ORDER BY clause in set operations
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 8 - 24
Matching the SELECT Statements
•
•
Using the UNION operator, display the location ID,
department name, and the state where it is located.
You must match the data type (using the TO_CHAR
function or any other conversion functions) when columns
do not exist in one or the other table.
SELECT location_id, department_name "Department",
TO_CHAR(NULL) "Warehouse location"
FROM departments
UNION
SELECT location_id, TO_CHAR(NULL) "Department",
state_province
FROM locations;
Copyright © 2009, Oracle. All rights reserved.
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Matching the SELECT Statements
Because the expressions in the SELECT lists of the queries must match in number, you can use the
dummy columns and the data type conversion functions to comply with this rule. In the slide, the
name, Warehouse location, is given as the dummy column heading. The TO_CHAR function is
used in the first query to match the VARCHAR2 data type of the state_province column that is
retrieved by the second query. Similarly, the TO_CHAR function in the second query is used to match
the VARCHAR2 data type of the department_name column that is retrieved by the first query.
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The output of the query is shown:
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Oracle Database 11g: SQL Fundamentals I 8 - 25
Matching the SELECT Statement: Example
Using the UNION operator, display the employee ID, job ID, and
salary of all employees.
SELECT
FROM
UNION
SELECT
FROM
employee_id, job_id,salary
employees
employee_id, job_id,0
job_history;
…
Copyright © 2009, Oracle. All rights reserved.
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Matching the SELECT Statement: Example
The EMPLOYEES and JOB_HISTORY tables have several columns in common (for example,
EMPLOYEE_ID, JOB_ID, and DEPARTMENT_ID). But what if you want the query to display the
employee ID, job ID, and salary using the UNION operator, knowing that the salary exists only in the
EMPLOYEES table?
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The code example in the slide matches the EMPLOYEE_ID and JOB_ID columns in the
EMPLOYEES and JOB_HISTORY tables. A literal value of 0 is added to the JOB_HISTORY
SELECT statement to match the numeric SALARY column in the EMPLOYEES SELECT statement.
In the results shown in the slide, each row in the output that corresponds to a record from the
JOB_HISTORY table contains a 0 in the SALARY column.
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Oracle Database 11g: SQL Fundamentals I 8 - 26
Lesson Agenda
•
•
•
•
•
•
•
Set Operators: Types and guidelines
Tables used in this lesson
UNION and UNION ALL operator
INTERSECT operator
MINUS operator
Matching the SELECT statements
Using the ORDER BY clause in set operations
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Copyright © 2009, Oracle. All rights reserved.
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Oracle Database 11g: SQL Fundamentals I 8 - 27
Using the ORDER BY Clause in Set Operations
•
•
The ORDER BY clause can appear only once at the end of
the compound query.
Component queries cannot have individual ORDER BY
clauses.
ORDER BY clause recognizes only the columns of the first
SELECT query.
By default, the first column of the first SELECT query is
used to sort the output in an ascending order.
•
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Copyright © 2009, Oracle. All rights reserved.
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Using the ORDER BY Clause in Set Operations
The ORDER BY clause can be used only once in a compound query. If used, the ORDER BY clause
must be placed at the end of the query. The ORDER BY clause accepts the column name or an alias.
By default, the output is sorted in ascending order in the first column of the first SELECT query.
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Note: The ORDER BY clause does not recognize the column names of the second SELECT query. To
avoid confusion over column names, it is a common practice to ORDER BY column positions.
For example, in the following statement, the output will be shown in ascending order of the job_id.
SELECT employee_id, job_id,salary
FROM
employees
UNION
SELECT employee_id, job_id,0
FROM
job_history
ORDER BY 2;
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If you omit the ORDER BY, then by default the output will be sorted in the ascending order of
employee_id. You cannot use the columns from the second query to sort the output.
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Oracle Database 11g: SQL Fundamentals I 8 - 28
Quiz
Identify the set operator guidelines.
1. The expressions in the SELECT lists must match in
number.
2. Parentheses may not be used to alter the sequence of
execution.
3. The data type of each column in the second query must
match the data type of its corresponding column in the first
query.
4. The ORDER BY clause can be used only once in a
compound query, unless a UNION ALL operator is used.
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Copyright © 2009, Oracle. All rights reserved.
Answer: 1, 3
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Oracle Database 11g: SQL Fundamentals I 8 - 29
Summary
In this lesson, you should have learned how to use:
• UNION to return all distinct rows
• UNION ALL to return all rows, including duplicates
• INTERSECT to return all rows that are shared by both
queries
• MINUS to return all distinct rows that are selected by the
first query, but not by the second
• ORDER BY only at the very end of the statement
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Copyright © 2009, Oracle. All rights reserved.
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Summary
• The UNION operator returns all the distinct rows selected by each query in the compound query.
Use the UNION operator to return all rows from multiple tables and eliminate any duplicate
rows.
• Use the UNION ALL operator to return all rows from multiple queries. Unlike the case with the
UNION operator, duplicate rows are not eliminated and the output is not sorted by default.
• Use the INTERSECT operator to return all rows that are common to multiple queries.
• Use the MINUS operator to return rows returned by the first query that are not present in the
second query.
• Remember to use the ORDER BY clause only at the very end of the compound statement.
• Make sure that the corresponding expressions in the SELECT lists match in number and data
type.
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Oracle Database 11g: SQL Fundamentals I 8 - 30
Practice 8: Overview
In this practice, you create reports by using:
• The UNION operator
• The INTERSECTION operator
• The MINUS operator
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Copyright © 2009, Oracle. All rights reserved.
Practice 8: Overview
In this practice, you write queries using the set operators.
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Oracle Database 11g: SQL Fundamentals I 8 - 31
Practice 8
1. The HR department needs a list of department IDs for departments that do not contain the job
ID ST_CLERK. Use the set operators to create this report.
2. The HR department needs a list of countries that have no departments located in them. Display
the country ID and the name of the countries. Use the set operators to create this report.
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3. Produce a list of jobs for departments 10, 50, and 20, in that order. Display the job ID and
department ID by using the set operators.
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4. Create a report that lists the employee IDs and job IDs of those employees who currently have a
job title that is the same as their job title when they were initially hired by the company (that is,
they changed jobs but have now gone back to doing their original job).
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Oracle Database 11g: SQL Fundamentals I 8 - 32
Practice 8 (continued)
5. The HR department needs a report with the following specifications:
• Last name and department ID of all employees from the EMPLOYEES table, regardless of
whether or not they belong to a department
• Department ID and department name of all departments from the DEPARTMENTS table,
regardless of whether or not they have employees working in them
Write a compound query to accomplish this.
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Oracle Database 11g: SQL Fundamentals I 8 - 33
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