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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Cover Page
Table of Contents
Preface
Introduction
Lesson 1: Retrieving Data Using the SQL SELECT Statement
Lesson 2: Restricting and Sorting Data
Lesson 3: Using Single-Row Functions to Customize Output
Lesson 4: Using Conversion Functions and Conditional Expressions
Lesson 5: Reporting Aggregated Data Using the Group Functions
Lesson 6: Displaying Data from Multiple Tables
Lesson 7: Using Subqueries to Solve Queries
Lesson 8: Using the Set Operators

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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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Disclaimer

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

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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,

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Authors

Puja Singh

Brian Pottle

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

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

2 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

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

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

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

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

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

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

8 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

UNION ALL Operator 8-16

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

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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Preface - 3

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 - 4

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 - 5

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, Use the SELECT command to view

functions, information stored in the LAST_NAME

column names, column of the EMPLOYEES table.

table names,

PL/SQL objects,

schemas

Lowercase, Filenames, where: role is the name of the role

italic syntax variables, to be created.

usernames,

passwords

Initial cap Trigger and Assign a When-Validate-Item trigger to

button names the ORD block.

Choose Cancel.

Italic Books, names of For more information on the subject see

courses and Oracle SQL Reference

manuals, and Manual

emphasized

words or phrases Do not save changes to the database.

Quotation marks Lesson module This subject is covered in Lesson 3,

titles referenced “Working with Objects.”

within a course

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Preface - 6

Typographic Conventions (continued)

Typographic Conventions Within Code

Convention Object or Term Example

Uppercase Commands, SELECT employee_id

functions FROM employees;

Lowercase, Syntax variables CREATE ROLE role;

italic

Initial cap Forms triggers Form module: ORD

Trigger level: S_ITEM.QUANTITY

item

Trigger name: When-Validate-Item

. . .

Lowercase Column names, . . .

table names, OG_ACTIVATE_LAYER

filenames, (OG_GET_LAYER ('prod_pie_layer'))

PL/SQL objects . . .

SELECT last_name

FROM employees;

Bold Text that must CREATE USER scott

be entered by a IDENTIFIED BY tiger;

user

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Introduction

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Oracle Database 11g: SQL Fundamentals I I - 2

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

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 - 3

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 11gdocumentation and additional

resources

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Oracle Database 11g: SQL Fundamentals I I - 4

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

Course Objectives

This course offers you an introduction to Oracle Database 11gdatabase 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 - 5

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 - 6

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 - 7

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 - 8

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 11gdocumentation and additional

resources

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Oracle Database 11g: SQL Fundamentals I I - 9

Oracle Database 11g: Focus Areas

Infrastructure

Grids

Information

Management

Application

Development

Oracle Database 11g: Focus Areas

Oracle Database 11goffers 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 11gconsolidates and

extends the benefits of grid computing. Apart from taking full advantage of grid computing,

Oracle Database 11ghas unique change assurance features to manage changes in a controlled

and cost effective manner.

•Information Management: Oracle Database 11gextends 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 - 10

Oracle Database 11g

Manageability

High availability

Performance

Security

Information integration

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

Manageability

High availability

Performance

Security

Information integration

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 11genables

organizations to manage large, scalable transactional and data warehousing systems that deliver

fast data access using low-cost modular storage.

•Security: Oracle Database 11ghelps 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 11ghas 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 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

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 Enterprise Manager Grid Control 10g

•Efficient Oracle Fusion Middleware management

•Simplifying application and infrastructure life cycle

management

•Improved database administration and application

management capabilities

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 10gfeatures 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 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.

BI PUBLISHER

PDF

HTML

Excel

Microsoft Word

Oracle BI Publisher

Oracle Database 11galso 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.

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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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 11gdocumentation and additional

resources

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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

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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Data Storage on Different Media

Electronic

spreadsheet Filing cabinet Database

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.

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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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

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.

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 user-

interface 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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Definition of a Relational Database

A relational database is a collection of relations or

two-dimensional tables.

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server

Table name: EMPLOYEES Table name: DEPARTMENTS

……

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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Data Models

Model of

system

in client’s

mind

Entity model of

client’s model

Tables on disk

Oracle

server

Table model

of entity model

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.

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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Entity Relationship Model

•Create an entity relationship diagram from business

specifications or narratives:

•Scenario:

–“. . . Assign one or more employees to a

department . . .”

–“. . . Some departments do not yet have assigned employees

. . .”

EMPLOYEE

#* number

*name

o job title

DEPARTMENT

#* number

*name

olocation

assigned to

composed of

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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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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Entity Relationship

Modeling Conventions

Entity:

•Singular, unique name

•Uppercase

•Soft box

•Synonym in parentheses

Unique Identifier (UID)

Primary marked with “#”

Secondary marked with “(#)”

EMPLOYEE

#* number

*name

o job title

DEPARTMENT

#* number

*name

olocation

assigned to

composed of

Attribute:

•Singular name

•Lowercase

•Mandatory marked with “*”

•Optional marked with “o”

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

Symbol Description

Dashed line Optional element indicating “maybe”

Solid line Mandatory element indicating “must be”

Crow’s foot Degree element indicating “one or more”

Single line Degree element indicating “one and only one”

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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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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: EMPLOYEES

Table name: DEPARTMENTS

Primary key Primary keyForeign key

…

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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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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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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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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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 11gdocumentation and additional

resources

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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;

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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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SQL Statements

SELECT

INSERT

UPDATE

DELETE

MERGE

CREATE

ALTER

DROP

RENAME

TRUNCATE

COMMENT

GRANT

REVOKE

COMMIT

ROLLBACK

SAVEPOINT

Data manipulation language (DML)

Data definition language (DDL)

Transaction control

Data control language (DCL)

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.

Statement Description

SELECT

INSERT

UPDATE

DELETE

MERGE

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)

CREATE

ALTER

DROP

RENAME

TRUNCATE

COMMENT

Sets up, changes, and removes data structures from tables. Collectively known as

data definition language (DDL)

GRANT

REVOKE Provides or removes access rights to both the Oracle database and the structures

within it

COMMIT

ROLLBACK

SAVEPOINT

Manages the changes made by DML statements. Changes to the data can be

grouped together into logical transactions

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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

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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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 11gdocumentation and additional

resources

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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

COUNTRIES

country_id

country_name

region_id

REGIONS

region_id

region_name

EMPLOYEES

employee_id

first_name

last_name

phone_number

hire_date

job_id

salary

commission_pct

manager_id

department_id

JOBS

job_id

job_title

min_salary

max_salary

JOB_HISTORY

employee_id

start_date

end_date

job_id

department_id

The Human Resources (HR)Schema Description

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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Tables Used in the Course

EMPLOYEES

DEPARTMENTS JOB_GRADES

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

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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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 11gdocumentation and additional

resources

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Oracle Database 11gDocumentation

•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

Oracle Database 11gDocumentation

Navigate to http://www.oracle.com/pls/db111/homepage to access the Oracle Database 11g

documentation library.

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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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Summary

In this lesson, you should have learned that:

•Oracle Database 11gextends:

–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

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 11gwith 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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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

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.

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 - 41

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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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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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

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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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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Capabilities of SQL SELECT Statements

Selection

Projection

Table 1 Table 2

Table 1

Join

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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Basic SELECT Statement

•SELECT identifies the columns to be displayed.

•FROM identifies the table containing those columns.

SELECT *|{[DISTINCT] column|expression [alias],...}

FROM table;

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

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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Selecting All Columns

SELECT *

FROM departments;

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 department_id, department_name, manager_id, location_id

FROM 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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Selecting Specific Columns

SELECT department_id, location_id

FROM departments;

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:

SELECT location_id, department_id

FROM departments;

…

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Writing SQL Statements

•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 (;).

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.

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.

In SQL*Plus, terminate the SQL statement with a semicolon, and then press [Enter] to run the

command.

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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

Column Heading Defaults

In SQL Developer, column headings are displayed in uppercase and are left-aligned.

SELECT last_name, hire_date, salary

FROM employees;

You can override the column heading display with an alias. Column aliases are covered later in this

lesson.

…

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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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Arithmetic Expressions

Create expressions with number and date data by using

arithmetic operators.

Multiply*

Divide/

Subtract-

Add+

DescriptionOperator

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.

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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SELECT last_name, salary, salary + 300

FROM employees;

Using Arithmetic Operators

…

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.

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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SELECT last_name, salary, 12*salary+100

FROM employees;

Operator Precedence

SELECT last_name, salary, 12*(salary+100)

FROM employees;

…

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.

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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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;

…

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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SELECT last_name, 12*salary*commission_pct

FROM employees;

Null Values in Arithmetic Expressions

Arithmetic expressions containing a null value evaluate to null.

…

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.

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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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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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

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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Using Column Aliases

SELECT last_name "Name" , salary*12 "Annual Salary"

FROM employees;

SELECT last_name AS name, commission_pct comm

FROM employees;

…

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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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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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 last_name||job_id AS "Employees"

FROM employees;

…

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.

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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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.

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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Using Literal Character Strings

…

SELECT last_name ||' is a '||job_id

AS "Employee Details"

FROM employees;

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.

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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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;

Alternative Quote (q) Operator

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 qoperator, 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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Duplicate Rows

The default display of queries is all rows, including duplicate

rows.

SELECT department_id

FROM employees;

SELECT DISTINCT department_id

FROM employees;

…

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 DISTINCT department_id, job_id

FROM employees;

…

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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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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

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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Using the DESCRIBE Command

DESCRIBE employees

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 Description

NUMBER(p,s)

Number value having a maximum number of digits p, with s

digits to the right of the decimal point

VARCHAR2(s) Variable-length character value of maximum size s

DATE Date and time value between January 1, 4712 B.C. and

December 31, A.D. 9999.

CHAR(s) Fixed-length character value of size s

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Quiz

Identify the SELECT statements that execute successfully.

SELECT first_name, last_name, job_id, salary*12

AS Yearly Sal

FROM employees;

SELECT first_name, last_name, job_id, salary*12

yearly sal

FROM employees;

SELECT first_name, last_name, job_id, salary AS

yearly sal

FROM employees;

SELECT first_name+last_name AS name, job_Id,

salary*12 yearly sal

FROM employees;

Answer: 2, 3

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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;

Summary

In this lesson, you should have learned how to retrieve data from a database table with the SELECT

statement.

SELECT *|{[DISTINCT] column [alias],...}

FROM table;

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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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

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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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 employee_id, last_name

sal x 12 ANNUAL SALARY

FROM 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_<lessonno>_<stepno>.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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Practice 1 (continued)

Part 2 (continued)

5. You need to determine the structure of the EMPLOYEES table.

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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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.

7. The HR department wants a query to display all unique job IDs from the EMPLOYEES table.

…

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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.

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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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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Restricting and Sorting Data

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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

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

This lesson explains the SQL statements that you use to perform the actions listed above.

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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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Limiting Rows Using a Selection

“retrieve all

employees in

department 90”

EMPLOYEES

…

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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Limiting the Rows That Are Selected

•Restrict the rows that are returned by using the WHERE

clause:

•The WHERE clause follows the FROM clause.

SELECT *|{[DISTINCT] column|expression [alias],...}

FROM table

[WHERE condition(s)];

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 restricts the query to rows that meet a condition

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

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SELECT employee_id, last_name, job_id, department_id

FROM employees

WHERE department_id = 90 ;

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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SELECT last_name, job_id, department_id

FROM employees

WHERE last_name = 'Whalen' ;

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

FROM employees

WHERE hire_date = '17-FEB-96' ;

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:

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 single-

row functions such as UPPER and LOWER to override the case sensitivity in the same lesson.

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Comparison Operators

Not equal to<>

Between two values (inclusive)

BETWEEN

...AND...

Match any of a list of values

IN(set)

Match a character pattern

Is a null value

IS NULL

Less than<

Less than or equal to<=

Greater than or equal to>=

Greater than>

Equal to=

MeaningOperator

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

... 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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SELECT last_name, salary

FROM employees

WHERE salary <= 3000 ;

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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SELECT last_name, salary

FROM employees

WHERE salary BETWEEN 2500 AND 3500 ;

Range Conditions Using the BETWEEN Operator

Use the BETWEEN operator to display rows based on a range of

values:

Lower limit Upper limit

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.

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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SELECT employee_id, last_name, salary, manager_id

FROM employees

WHERE manager_id IN (100, 101, 201) ;

Membership Condition Using the IN Operator

Use the IN operator to test for values in a list:

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.

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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SELECT first_name

FROM employees

WHERE first_name LIKE 'S%' ;

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.

Pattern Matching Using the LIKE Operator

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.

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:

SELECT last_name, hire_date

FROM employees

WHERE hire_date LIKE '%95';

Symbol Description

% Represents any sequence of zero or more characters

_ Represents any single character

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Combining Wildcard Characters

•You can combine the two wildcard characters (%, _) with

literal characters for pattern matching:

•You can use the ESCAPE identifier to search for the actual

%and _symbols.

SELECT last_name

FROM employees

WHERE last_name LIKE '_o%' ;

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:

SELECT employee_id, last_name, job_id

FROM employees WHERE job_id LIKE '%SA\_%' ESCAPE '\';

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.

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SELECT last_name, manager_id

FROM employees

WHERE manager_id IS NULL ;

Using the NULL Conditions

Test for nulls with the IS NULL operator.

Using the NULL Conditions

The NULL conditions include the IS NULL condition and the IS NOT NULL condition.

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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Defining Conditions Using the Logical Operators

Returns TRUE if the condition is false

NOT

Returns TRUE if either component condition

is true

Returns TRUE if both component conditions

are true

AND

MeaningOperator

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.

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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SELECT employee_id, last_name, job_id, salary

FROM employees

WHERE salary >= 10000

AND job_id LIKE '%MAN%' ;

Using the AND Operator

AND requires both the component conditions to be true:

Using the AND Operator

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

TRUE TRUE FALSE NULL

FALSE FALSE FALSE FALSE

NULL NULL FALSE NULL

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SELECT employee_id, last_name, job_id, salary

FROM employees

WHERE salary >= 10000

OR job_id LIKE '%MAN%' ;

Using the OR Operator

OR requires either component condition to be true:

Using the OR Operator

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

FALSE TRUE FALSE NULL

NULL TRUE NULL NULL

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SELECT last_name, job_id

FROM employees

WHERE job_id

NOT IN ('IT_PROG', 'ST_CLERK', 'SA_REP') ;

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:

Note: The NOT operator can also be used with other SQL operators, such as BETWEEN, LIKE, and

NULL.

... WHERE job_id NOT IN ('AC_ACCOUNT', 'AD_VP')

... WHERE salary NOT BETWEEN 10000 AND 15000

... WHERE last_name NOT LIKE '%A%'

... WHERE commission_pct IS NOT NULL

NOT TRUE FALSE NULL

FALSE TRUE NULL

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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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Rules of Precedence

You can use parentheses to override rules of precedence.

Not equal to6

NOT logical condition

AND logical condition

OR logical condition

IS [NOT] NULL, LIKE, [NOT] IN

[NOT] BETWEEN

Comparison conditions3

Concatenation operator2

Arithmetic operators1

MeaningOperator

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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SELECT last_name, job_id, salary

FROM employees

WHERE job_id = 'SA_REP'

OR job_id = 'AD_PRES'

AND salary > 15000;

Rules of Precedence

SELECT last_name, job_id, salary

FROM employees

WHERE (job_id = 'SA_REP'

OR job_id = 'AD_PRES')

AND salary > 15000;

Rules of Precedence (continued)

1. Precedence of the AND Operator: Example

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:

“Select the row if an employee is a president or a sales representative, and if the employee earns

more than $15,000.”

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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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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 ;

…

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 expr

FROM table

[WHERE condition(s)]

[ORDER BY {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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Sorting

•Sorting in descending order:

•Sorting by column alias:

SELECT last_name, job_id, department_id, hire_date

FROM employees

ORDER BY hire_date DESC ; 1

SELECT employee_id, last_name, salary*12 annsal

FROM employees

ORDER BY annsal ; 2

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.

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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Sorting

•Sorting by using the column’s numeric position:

•Sorting by multiple columns:

SELECT last_name, job_id, department_id, hire_date

FROM employees

ORDER BY 3; 3

SELECT last_name, department_id, salary

FROM employees

ORDER BY department_id, salary DESC; 4

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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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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Substitution Variables

... salary = ? …

… department_id = ? …

... last_name = ? ...

I want

to query

different

values.

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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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

Substitution Variables (continued)

You can use single-ampersand (&) substitution variables to temporarily store values.

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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SELECT employee_id, last_name, salary, department_id

FROM employees

WHERE employee_id = &employee_num ;

Using the Single-Ampersand Substitution

Variable

Use a variable prefixed with an ampersand (&) to prompt the

user for a value:

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.

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.

Notation Description

&user_variable Indicates a variable in a SQL statement; if the variable

does not exist, SQL*Plus or SQL Developer prompts the

user for a value (the new variable is discarded after it is

used.)

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Using the Single-Ampersand Substitution

Variable

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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SELECT last_name, department_id, salary*12

FROM employees

WHERE job_id = '&job_title' ;

Character and Date Values with

Substitution Variables

Use single quotation marks for date and character values:

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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Specifying Column Names,

Expressions, and Text

SELECT employee_id, last_name, job_id,&column_name

FROM employees

WHERE &condition

ORDER BY &order_column ;

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.

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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SELECT employee_id, last_name, job_id, &&column_name

FROM employees

ORDER BY &column_name ;

…

Using the Double-Ampersand

Substitution Variable

Use double ampersand (&&) if you want to reuse the variable

value without prompting the user each time:

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:

UNDEFINE column_name

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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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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

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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SET VERIFY ON

SELECT employee_id, last_name, salary

FROM employees

WHERE employee_id = &employee_num;

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:

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.

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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Quiz

Which of the following are valid operators for the WHERE

clause?

1. >=

2. IS NULL

3. !=

4. IS LIKE

5. IN BETWEEN

6. <>

Answer: 1, 2, 3, 6

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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:

•Use ampersand substitution to restrict and sort output at

run time

SELECT *|{[DISTINCT] column|expression [alias],...}

FROM table

[WHERE condition(s)]

[ORDER BY {column, expr, alias} [ASC|DESC]] ;

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.

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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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

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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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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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.

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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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.

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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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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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.

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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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

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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Lesson Agenda

•Single-row SQL functions

• Character functions

• Number functions

• Working with dates

• Date functions

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SQL Functions

Function

Input

arg 1

arg 2

arg n

Function performs

action

Output

Result

value

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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Two Types of SQL Functions

Single-row

functions

Multiple-row

functions

Return one result

per row

Return one result

per set of rows

Functions

Two Types of SQL Functions

There are two types of functions:

• Single-row functions

• Multiple-row functions

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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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,...)]

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

In the syntax:

function_name is the name of the function

arg1, arg2 is any argument to be used by the function. This can be

represented by a column name or expression.

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Single-Row Functions

Conversion

Character

Number

Date

General Single-row

functions

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.)

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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Lesson Agenda

• Single-row SQL functions

•Character functions

• Number functions

• Working with dates

• Date functions

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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.)

Character Functions

Character

functions

LOWER

UPPER

INITCAP

CONCAT

SUBSTR

LENGTH

INSTR

LPAD | RPAD

TRIM

REPLACE

Case-conversion

functions

Character-manipulation

functions

Character Functions

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

Note: The functions discussed in this lesson are only some of the available functions.

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Character Functions (continued)

Note: Some of the functions that are fully or partially SQL:2003 compliant are:

UPPER

LOWER

TRIM

LENGTH

SUBSTR

INSTR

Refer to the Oracle Compliance To Core SQL:2003 section in Oracle Database SQL Language

Reference 11g, Release 1 (11.1) for more information.

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.

LPAD(column|expression, n,

'string')

RPAD(column|expression, n,

'string')

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.

TRIM(leading|trailing|both,

trim_character FROM

trim_source)

Enables you to trim leading or trailing characters (or

both) from a character string. If trim_character or

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

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Case-Conversion Functions

These functions convert the case for character strings:

sql courseLOWER('SQL Course')

Sql Course

INITCAP('SQL Course')

SQL COURSEUPPER('SQL Course')

ResultFunction

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

SELECT 'The job id for '||UPPER(last_name)||' is '

||LOWER(job_id) AS "EMPLOYEE DETAILS"

FROM employees;

…

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SELECT employee_id, last_name, department_id

FROM employees

WHERE LOWER(last_name) = 'higgins';

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';

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:

...WHERE last_name = 'Higgins'

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.

SELECT employee_id, UPPER(last_name), department_id

FROM employees

WHERE INITCAP(last_name) = 'Higgins';

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Character-Manipulation Functions

These functions manipulate character strings:

BLACK and BLUE REPLACE

('JACK and JUE','J','BL')

10LENGTH('HelloWorld')

6INSTR('HelloWorld', 'W')

*****24000LPAD(salary,10,'*')

24000*****RPAD(salary, 10, '*')

HelloWorldCONCAT('Hello', 'World')

elloWorldTRIM('H' FROM 'HelloWorld')

HelloSUBSTR('HelloWorld',1,5)

ResultFunction

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 ncharacters 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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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';

Using the Character-Manipulation Functions

31 2

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 employee_id, CONCAT(first_name, last_name) NAME,

LENGTH (last_name), INSTR(last_name, 'a') "Contains 'a'?"

FROM employees

WHERE SUBSTR(last_name, -1, 1) = 'n';

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Lesson Agenda

• Single-row SQL functions

• Character functions

•Number functions

• Working with dates

• Date Functions

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Number Functions

•ROUND: Rounds value to a specified decimal

•TRUNC: Truncates value to a specified decimal

•MOD: Returns remainder of division

100MOD(1600, 300)

45.93ROUND(45.926, 2)

45.92TRUNC(45.926, 2)

ResultFunction

Number Functions

Number functions accept numeric input and return numeric values. This section describes some of

the number functions.

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).

Function Purpose

ROUND(column|expression, n)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

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SELECT ROUND(45.923,2), ROUND(45.923,0),

ROUND(45.923,-1)

FROM DUAL;

Using the ROUND Function

DUAL is a dummy table that you can use to view results

from functions and calculations.

Using the ROUND Function

The ROUND function rounds the column, expression, or value to ndecimal 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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Using the TRUNC Function

SELECT TRUNC(45.923,2), TRUNC(45.923),

TRUNC(45.923,-1)

FROM DUAL;

Using the TRUNC Function

The TRUNC function truncates the column, expression, or value to n decimal places.

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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SELECT last_name, salary, MOD(salary, 5000)

FROM employees

WHERE job_id = 'SA_REP';

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.

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.

Note: The MOD function is often used to determine whether a value is odd or even.

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Lesson Agenda

• Single-row SQL functions

• Character functions

• Number functions

•Working with dates

• Date functions

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SELECT last_name, hire_date

FROM employees

WHERE hire_date < '

'01-FEB-88';

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

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 DD-

MON-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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RR Date Format

Current Year

1995

2001

27-OCT-95

27-OCT-17

27-OCT-95

1995

2017

1995

1917

2017

2095

If two digits

of the

current

year are:

0–49

0–49 50–99

50–99

The return date is in

the current century

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

If the specified two-digit year is:

YY Format

RR FormatSpecified Date

Current Year

RR Date Format

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 Given Date Interpreted (RR) Interpreted (YY)

1994 27-OCT-95 1995 1995

1994 27-OCT-17 2017 1917

2001 27-OCT-17 2017 2017

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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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Using the SYSDATE Function

SYSDATE is a function that returns:

•Date

•Time

SELECT sysdate

FROM dual;

;

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.

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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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.

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.

You can perform the following operations:

Operation Result Description

date + number Date Adds a number of days to a date

date – number Date Subtracts a number of days from a date

date – date Number of days Subtracts one date from another

date + number/24 Date Adds a number of hours to a date

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SELECT last_name, (SYSDATE-hire_date)/7 AS WEEKS

FROM employees

WHERE department_id = 90;

Using Arithmetic Operators

with Dates

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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Lesson Agenda

• Single-row SQL functions

• Character functions

• Number functions

• Working with dates

•Date functions

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Date-Manipulation Functions

Next day of the date specified

NEXT_DAY

Last day of the month

LAST_DAY

Round date

ROUND

Truncate date

TRUNC

Number of months between two dates

MONTHS_BETWEEN

Add calendar months to date

ADD_MONTHS

ResultFunction

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 nnumber of calendar months to date. The value of nmust

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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Using Date Functions

'08-SEP-95'NEXT_DAY ('01-SEP-95','FRIDAY')

'28-FEB-95'LAST_DAY ('01-FEB-95')

19.6774194MONTHS_BETWEEN

('01-SEP-95','11-JAN-94')

‘29-FEB-96'ADD_MONTHS (‘31-JAN-96',1)

ResultFunction

Using Date Functions

In the slide example, the ADD_MONTHS function adds one month to the supplied date value, “31-

JAN-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.

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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Using ROUND and TRUNC Functions with Dates

Assume SYSDATE = '25-JUL-03':

01-JUL-03

TRUNC(SYSDATE ,'MONTH')

01-JAN-03TRUNC(SYSDATE ,'YEAR')

01-AUG-03ROUND(SYSDATE,'MONTH')

01-JAN-04ROUND(SYSDATE ,'YEAR')

ResultFunction

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.

SELECT employee_id, hire_date,

ROUND(hire_date, 'MONTH'), TRUNC(hire_date, 'MONTH')

FROM employees

WHERE hire_date LIKE '%97';

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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

Answer: 1, 3, 6, 7

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Summary

In this lesson, you should have learned how to:

•Perform calculations on data using functions

•Modify individual data items using functions

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

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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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

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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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.

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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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.”

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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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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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.

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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Using Conversion Functions and

Conditional Expressions

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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

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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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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Conversion Functions

Implicit data type

conversion

Explicit data type

conversion

Data type

conversion

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.

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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Implicit Data Type Conversion

In expressions, the Oracle server can automatically convert the

following:

NUMBER

VARCHAR2 or CHAR

DATEVARCHAR2 or CHAR

ToFrom

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 '01-

JAN-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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Implicit Data Type Conversion

For expression evaluation, the Oracle server can automatically

convert the following:

VARCHAR2 or CHAR

NUMBER

VARCHAR2 or CHAR

DATE

ToFrom

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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Explicit Data Type Conversion

NUMBER CHARACTER

TO_CHAR

TO_NUMBER

DATE

TO_CHAR

TO_DATE

Explicit Data Type Conversion

SQL provides three functions to convert a value from one data type to another:

Function Purpose

TO_CHAR(number|date,[ fmt],

[nlsparams]) Converts a number or date value to a VARCHAR2

character string with the format model fmt

Number conversion: The nlsparams

parameter specifies the following characters,

which are returned by number format elements:

• 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.

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Explicit Data Type Conversion

NUMBER CHARACTER

TO_CHAR

TO_NUMBER

DATE

TO_CHAR

TO_DATE

Explicit Data Type Conversion (continued)

Function Purpose

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.

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.

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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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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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Using the TO_CHAR Function with Dates

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

TO_CHAR(date, 'format_model')

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-Nov-

1999' 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.

SELECT employee_id, TO_CHAR(hire_date, 'MM/YY') Month_Hired

FROM employees

WHERE last_name = 'Higgins';

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Elements of the Date Format Model

Three-letter abbreviation of the day of the week

Full name of the day of the week

DAY

Two-digit value for the month

Full name of the month

MONTH

Three-letter abbreviation of the month

MON

Numeric day of the month

Full year in numbers

YYYY

Year spelled out (in English)

YEAR

ResultElement

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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.

IW Weeks in the year from ISO standard (1 to 53)

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Elements of the Date Format Model

•Time elements format the time portion of the date:

•Add character strings by enclosing them with double

quotation marks:

•Number suffixes spell out numbers:

DD "of" MONTH 12 of OCTOBER

ddspth fourteenth

HH24:MI:SS AM 15:45:32 PM

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 Description

AM or PM Meridian indicator

A.M. or P.M. Meridian indicator with periods

HH or HH12 or HH24 Hour of day, or hour (1–12), or hour (0–23)

MI Minute (0–59)

SS Second (0–59)

SSSSS Seconds past midnight (0–86399)

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Other Formats

Specifying Suffixes to Influence Number Display

Element Description

/ . , Punctuation is reproduced in the result.

“of the” Quoted string is reproduced in the result.

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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SELECT last_name,

TO_CHAR(hire_date, 'fmDD Month YYYY')

AS HIREDATE

FROM employees;

Using the TO_CHAR Function with Dates

…

Using the TO_CHAR Function with Dates

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;

Notice that the month follows the format model specified; in other words, the first letter is capitalized

and the rest are in lowercase.

…

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Using the TO_CHAR Function with Numbers

These are some of the format elements that you can use with

the TO_CHAR function to display a number value as a

character:

Prints a decimal point

Prints a comma as a thousands indicator

Places a floating dollar sign

Uses the floating local currency symbol

Represents a number

Forces a zero to be displayed

ResultElement

TO_CHAR(number, 'format_model')

Using the TO_CHAR Function with Numbers

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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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 1.234E+03

U Returns in the specified position the “Euro” (or

other) dual currency

U9999 €1234

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 1234.00

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SELECT TO_CHAR(salary, '$99,999.00') SALARY

FROM employees

WHERE last_name = 'Ernst';

Using the TO_CHAR Function with Numbers

Using the TO_CHAR Function with Numbers (continued)

• 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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Using the TO_NUMBER and TO_DATE Functions

•Convert a character string to a number format using the

TO_NUMBER function:

•Convert a character string to a date format using the

TO_DATE function:

•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.

TO_NUMBER(char[, 'format_model'])

TO_DATE(char[, 'format_model'])

Using the TO_NUMBER and TO_DATE Functions

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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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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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');

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).

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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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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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

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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SELECT last_name,

UPPER(CONCAT(SUBSTR (LAST_NAME, 1, 8), '_US'))

FROM employees

WHERE department_id = 60;

Nesting Functions

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.

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;

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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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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)

General Functions

These functions work with any data type and pertain to the use of null values 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).

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 argument expr1 can have any data type.

NULLIF Compares 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

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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')

NVL Function

To convert a null value to an actual value, use the NVL function.

Syntax

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

Data Type Conversion Example

NUMBER NVL(number_column,9)

DATE NVL(date_column, '01-JAN-95')

CHAR or VARCHAR2 NVL(character_column, 'Unavailable')

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SELECT last_name, salary, NVL(commission_pct, 0),

(salary*12) + (salary*12*NVL(commission_pct, 0)) AN_SAL

FROM employees;

Using the NVL Function

…

Using the NVL Function

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;

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.

…

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SELECT last_name, salary, commission_pct,

NVL2(commission_pct,

'SAL+COMM', 'SAL') income

FROM employees WHERE department_id IN (50, 80);

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

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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SELECT first_name, LENGTH(first_name) "expr1",

last_name, LENGTH(last_name) "expr2",

NULLIF(LENGTH(first_name), LENGTH(last_name)) result

FROM employees;

Using the NULLIF Function

…

12 3

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

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:

CASE WHEN expr1 = expr 2 THEN NULL ELSE expr1 END

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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.

Using the COALESCE Function

The COALESCE function returns the first non-null expression in the list.

Syntax

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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SELECT last_name, employee_id,

COALESCE(TO_CHAR(commission_pct),TO_CHAR(manager_id),

'No commission and no manager')

FROM employees;

Using the COALESCE Function

…

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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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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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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Conditional Expressions

•Provide the use of the IF-THEN-ELSE logic within a SQL

statement

•Use two methods:

–CASE expression

–DECODE function

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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CASE Expression

Facilitates conditional inquiries by doing the work of an

IF-THEN-ELSE statement:

CASE expr WHEN comparison_expr1 THEN return_expr1

[WHEN comparison_expr2 THEN return_expr2

WHEN comparison_exprn THEN return_exprn

ELSE else_expr]

END

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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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;

Using the CASE Expression

Facilitates conditional inquiries by doing the work of an

IF-THEN-ELSE statement:

…

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.

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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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])

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.

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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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;

Using the DECODE Function

…

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:

IF job_id = 'IT_PROG' THEN salary = salary*1.10

IF job_id = 'ST_CLERK' THEN salary = salary*1.15

IF job_id = 'SA_REP' THEN salary = salary*1.20

ELSE salary = salary

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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;

Using the DECODE Function

Display the applicable tax rate for each employee in

department 80:

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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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

Answer: 2

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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

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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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

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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Practice 4

1. Create a report that produces the following for each employee:

<employee last name> earns <salary> 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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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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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 Grade

AD_PRES A

ST_MAN B

IT_PROG C

SA_REP D

ST_CLERK E

None of the above 0

6. Rewrite the statement in the preceding exercise using the CASE syntax.

…

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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

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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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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What Are Group Functions?

Group functions operate on sets of rows to give one result per

group.

EMPLOYEES

Maximum salary in

EMPLOYEES table

…

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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Types of Group Functions

•AVG

•COUNT

•MAX

•MIN

•STDDEV

•SUM

•VARIANCE

Group

functions

Types of Group Functions

Each of the functions accepts an argument. The following table identifies the options that you can

use in the syntax:

Function Description

AVG([DISTINCT|ALL]n) Average value of n, ignoring null values

COUNT({*|[DISTINCT|ALL]expr

})

Number of rows, where expr evaluates to

something other than null (count all selected

rows using *, including duplicates and rows

with nulls)

MAX([DISTINCT|ALL]expr) Maximum value of expr, ignoring null values

MIN([DISTINCT|ALL]expr) Minimum value of expr, ignoring null values

STDDEV([DISTINCT|ALL]x) Standard deviation of n, ignoring null values

SUM([DISTINCT|ALL]n) Sum values of n, ignoring null values

VARIANCE([DISTINCT|ALL]x) Variance of n, ignoring null values

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SELECT group_function(column), ...

FROM table

[WHERE condition]

[ORDER BY column];

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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SELECT AVG(salary), MAX(salary),

MIN(salary), SUM(salary)

FROM employees

WHERE job_id LIKE '%REP%';

Using the AVG and SUM Functions

You can use AVG and SUM for numeric data.

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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SELECT MIN(hire_date), MAX(hire_date)

FROM employees;

Using the MIN and MAX Functions

You can use MIN and MAX for numeric, character, and date

data types.

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:

SELECT MIN(last_name), MAX(last_name)

FROM employees;

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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Using the COUNT Function

COUNT(*) returns the number of rows in a table:

COUNT(expr)returns the number of rows with non-null values

for expr:

SELECT COUNT(commission_pct)

FROM employees

WHERE department_id = 80;

SELECT COUNT(*)

FROM employees

WHERE department_id = 50;

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.

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.

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SELECT COUNT(DISTINCT department_id)

FROM employees;

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:

Using the DISTINCT Keyword

Use the DISTINCT keyword to suppress the counting of any duplicate values in a column.

The example in the slide displays the number of distinct department values that are in the

EMPLOYEES table.

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Group Functions and Null Values

Group functions ignore null values in the column:

The NVL function forces group functions to include null values:

SELECT AVG(commission_pct)

FROM employees;

SELECT AVG(NVL(commission_pct, 0))

FROM employees;

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.

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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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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Creating Groups of Data

EMPLOYEES

…

4400

9500

3500

6400

10033

Average salary in

EMPLOYEES table for

each department

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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Creating Groups of Data:

GROUP BY Clause Syntax

You can divide rows in a table into smaller groups by using the

GROUP BY clause.

SELECT column, group_function(column)

FROM table

[WHERE condition]

[GROUP BY group_by_expression]

[ORDER BY column];

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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SELECT department_id, AVG(salary)

FROM employees

GROUP BY department_id ;

Using the GROUP BY Clause

All columns in the SELECT list that are not in group functions

must be in the GROUP BY clause.

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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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 ;

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:

SELECT department_id, AVG(salary)

FROM employees

GROUP BY department_id

ORDER BY AVG(salary);

…

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Grouping by More than One Column

EMPLOYEES Add the salaries in the EMPLOYEES

table for each job, grouped by

department.

…

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:

SELECT department_id, job_id, sum(salary)

FROM employees

GROUP BY department_id, job_id

ORDER BY job_id;

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SELECT department_id, job_id, SUM(salary)

FROM employees

WHERE department_id > 40

GROUP BY department_id, job_id

ORDER BY department_id;

Using the GROUP BY Clause

on Multiple Columns

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.

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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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;

SELECT department_id, job_id, COUNT(last_name)

FROM employees

GROUP BY department_id;

A GROUP BY clause must be added to

count the last names for each

department_id.

Either add job_id in the GROUP BY or

remove the job_id column from the

SELECT list.

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:

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.

SELECT department_id, job_id, COUNT(last_name)

FROM employees

GROUP BY department_id, job_id;

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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 department_id, AVG(salary)

FROM employees

WHERE AVG(salary) > 8000

GROUP BY department_id;

Cannot use the

WHERE clause to

restrict groups

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:

SELECT department_id, AVG(salary)

FROM employees

GROUP BY department_id

HAVING AVG(salary) > 8000;

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Restricting Group Results

EMPLOYEES

…

The maximum salary per

department when it is

greater than $10,000

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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SELECT column, group_function

FROM table

[WHERE condition]

[GROUP BY group_by_expression]

[HAVING group_condition]

[ORDER BY column];

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.

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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SELECT department_id, MAX(salary)

FROM employees

GROUP BY department_id

HAVING MAX(salary)>10000 ;

Using the HAVING Clause

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 department_id, AVG(salary)

FROM employees

GROUP BY department_id

HAVING max(salary)>10000;

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SELECT job_id, SUM(salary) PAYROLL

FROM employees

WHERE job_id NOT LIKE '%REP%'

GROUP BY job_id

HAVING SUM(salary) > 13000

ORDER BY SUM(salary);

Using the HAVING Clause

Using the HAVING Clause (continued)

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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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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SELECT MAX(AVG(salary))

FROM employees

GROUP BY department_id;

Nesting Group Functions

Display the maximum average salary:

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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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.

Answer: 1, 3

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SELECT column, group_function

FROM table

[WHERE condition]

[GROUP BY group_by_expression]

[HAVING group_condition]

[ORDER BY column];

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

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.

Note: For a complete list of the group functions, see Oracle Database SQL Language Reference 11g,

Release 1 (11.1).

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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

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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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.

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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Practice 5 (continued)

6. Write a query to display the number of people with the same job.

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.

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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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.

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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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

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.

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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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

–Cross join

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Obtaining Data from Multiple Tables

EMPLOYEES DEPARTMENTS

…

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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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

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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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];

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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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.

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.

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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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

–Cross join

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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.

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.

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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SELECT department_id, department_name,

location_id, city

FROM departments

NATURAL JOIN locations ;

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:

SELECT department_id, department_name,

location_id, city

FROM departments

NATURAL JOIN locations

WHERE department_id IN (20, 50);

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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.

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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Joining Column Names

EMPLOYEES DEPARTMENTS

Foreign key

Primary key

…

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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SELECT employee_id, last_name,

location_id, department_id

FROM employees JOIN departments

USING (department_id) ;

Retrieving Records with the USING Clause

…

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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SELECT l.city, d.department_name

FROM locations l JOIN departments d

USING (location_id)

WHERE d.location_id = 1400;

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.

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.

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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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.

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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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);

Retrieving Records with the ON Clause

…

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.

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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SELECT employee_id, city, department_name

FROM employees e

JOIN departments d

ON d.department_id = e.department_id

JOIN locations l

ON d.location_id = l.location_id;

Creating Three-Way Joins with

the ON Clause

…

Creating Three-Way Joins with the ON Clause

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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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 ;

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)

WHERE e.manager_id = 149 ;

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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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

–Cross join

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Joining a Table to Itself

MANAGER_ID in the WORKER table is equal to

EMPLOYEE_ID in the MANAGER table.

EMPLOYEES (WORKER) EMPLOYEES (MANAGER)

……

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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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);

…

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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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

–Cross join

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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.

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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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;

Retrieving Records

with Nonequijoins

…

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.

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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Lesson Agenda

• Types of JOINS and its syntax

• Natural join:

–USING clause

–ON clause

• Self-join

• Nonequijo

uijoins

•OUTER join:

–LEFT OUTER join

–RIGHT OUTER join

–FULL OUTER join

• Cartesian product

–Cross join

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Returning Records with No Direct Match

Using OUTER Joins

Equijoin with EMPLOYEES

DEPARTMENTS

There are no employees

in department 190.

Employee “Grant” has

not been assigned a

department ID.

…

Returning Records with No Direct Match Using OUTER Joins

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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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.

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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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) ;

LEFT OUTER JOIN

…

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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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) ;

RIGHT OUTER JOIN

…

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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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) ;

FULL OUTER JOIN

…

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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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

–Cross join

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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.

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.

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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Generating a Cartesian Product

Cartesian product:

20 x 8 = 160 rows

EMPLOYEES (20 rows) DEPARTMENTS (8 rows)

…

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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SELECT last_name, department_name

FROM employees

CROSS JOIN departments ;

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.

…

Creating Cross Joins

The example in the slide produces a Cartesian product of the EMPLOYEES and DEPARTMENTS

tables.

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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

Answer: 1, 2, 3, 4, 6, 8

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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

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

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.

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.

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Practice 6: Overview

This practice covers the following topics:

•Joining tables using an equijoin

•Performing outer and self-joins

•Adding conditions

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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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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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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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.

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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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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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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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

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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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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Using a Subquery to Solve a Problem

Who has a salary greater than Abel’s?

Which employees have salaries greater than Abel’s

salary?

Main query:

What is Abel’s salary?

Subquery:

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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Subquery Syntax

•The subquery (inner query) executes before the main

query (outer query).

•The result of the subquery is used by the main query.

SELECT select_list

FROM table

WHERE expr operator

(SELECT select_list

FROM table);

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

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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SELECT last_name, salary

FROM employees

WHERE salary >

(SELECT salary

FROM employees

WHERE last_name = 'Abel');

Using a Subquery

11000

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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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.

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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Types of Subqueries

•Single-row subquery

•Multiple-row subquery

Main query

Subquery returns ST_CLERK

ST_CLERK

SA_MAN

Main query

Subquery returns

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

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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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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Single-Row Subqueries

•Return only one row

•Use single-row comparison operators

Greater than or equal to

Less than

Less than or equal to

Equal to

Not equal to

Greater than

MeaningOperator

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:

SELECT last_name, job_id

FROM employees

WHERE job_id =

(SELECT job_id

FROM employees

WHERE employee_id = 141);

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SELECT last_name, job_id, salary

FROM employees

WHERE job_id =

(SELECT job_id

FROM employees

WHERE last_name = ‘Taylor’)

AND salary >

(SELECT salary

FROM employees

WHERE last_name = ‘Taylor’);

Executing Single-Row Subqueries

SA_REP

8600

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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SELECT last_name, job_id, salary

FROM employees

WHERE salary =

(SELECT MIN(salary)

FROM employees);

Using Group Functions in a Subquery

2500

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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SELECT department_id, MIN(salary)

FROM employees

GROUP BY department_id

HAVING MIN(salary) >

(SELECT MIN(salary)

FROM employees

WHERE department_id = 50);

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.

2500

…

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.

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 job_id, AVG(salary)

FROM employees

GROUP BY job_id

HAVING AVG(salary) = (SELECT MIN(AVG(salary))

FROM employees

GROUP BY job_id);

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SELECT employee_id, last_name

FROM employees

WHERE salary =

(SELECT MIN(salary)

FROM employees

GROUP BY department_id);

What Is Wrong with This Statement?

Single-row operator

with multiple-row

subquery

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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SELECT last_name, job_id

FROM employees

WHERE job_id =

(SELECT job_id

FROM employees

WHERE last_name = 'Haas');

No Rows Returned by the Inner Query

Subquery returns no rows because there is no

employee named “Haas.”

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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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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Multiple-Row Subqueries

•Return more than one row

•Use multiple-row comparison operators

Must be preceded by =, !=, >, <, <=, >=.

Compares a value to every value in a list or

returned by a query. Evaluates to TRUE if the

query returns no rows.

ALL

Equal to any member in the list

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.

ANY

MeaningOperator

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:

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:

SELECT last_name, salary, department_id

FROM employees

WHERE salary IN (2500, 4200, 4400, 6000, 7000, 8300,

8600, 17000);

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SELECT employee_id, last_name, job_id, salary

FROM employees

WHERE salary < ANY

(SELECT salary

FROM employees

WHERE job_id = 'IT_PROG')

AND job_id <> 'IT_PROG';

Using the ANY Operator

in Multiple-Row Subqueries

9000, 6000, 4200

…

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 less than the maximum. >ANY means more than the minimum. =ANY is equivalent to

IN.

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SELECT employee_id, last_name, job_id, salary

FROM employees

WHERE salary < ALL

(SELECT salary

FROM employees

WHERE job_id = 'IT_PROG')

AND job_id <> 'IT_PROG';

Using the ALL Operator

in Multiple-Row Subqueries

9000, 6000, 4200

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.

>ALL means more than the maximum and <ALL means less than the minimum.

The NOT operator can be used with IN, ANY, and ALL operators.

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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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SELECT emp.last_name

FROM employees emp

WHERE emp.employee_id NOT IN

(SELECT mgr.manager_id

FROM employees mgr);

Null Values in a Subquery

The SQL statement in the slide attempts to display all the employees who do not have any

subordinates. Logically, this SQL statement should have returned 12 rows. However, the SQL

statement does not return any rows. One of the values returned by the inner query is a null value, and,

therefore, the entire query returns no rows.

The reason is that all conditions that compare a null value result in a null. So whenever null values

are likely to be part of the results set of a subquery, do not use the NOT IN operator. The NOT IN

operator is equivalent to <> 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 IN

(SELECT mgr.manager_id

FROM employees mgr);

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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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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

Answer: 1

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SELECT select_list

FROM table

WHERE expr operator

(SELECT select_list

FROM table);

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

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.

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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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

Practice 7: Overview

In this practice, you write complex queries using nested SELECT statements.

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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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).

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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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.

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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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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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

Objectives

In this lesson, you learn how to write queries by using set operators.

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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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Set Operators

UNION/UNION ALL

ABAB

INTERSECT

MINUS

Set Operators

Set operators combine the results of two or more component queries into one result. Queries

containing set operators are called compound queries.

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.

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

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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.

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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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.

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.

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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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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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

Tables Used in This Lesson

Two tables are used in this lesson. They are the EMPLOYEES table and the JOB_HISTORY table.

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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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 31-

DEC-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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Tables Used in This Lesson (continued)

SELECT employee_id, last_name, job_id, hire_date, department_id

FROM employees;

DESCRIBE job_history

…

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Tables Used in This Lesson (continued)

SELECT * FROM job_history;

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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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UNION Operator

A B

The UNION operator returns rows from both queries after eliminating

duplications.

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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Using the UNION Operator

Display the current and previous job details of all employees.

Display each employee only once.

SELECT employee_id, job_id

FROM employees

UNION

SELECT employee_id, job_id

FROM job_history;

…

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.

Consider the following example:

SELECT employee_id, job_id, department_id

FROM employees

UNION

SELECT employee_id, job_id, department_id

FROM job_history;

…

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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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UNION ALL Operator

The UNION ALL operator returns rows from both queries, including all

duplications.

A B

UNION ALL Operator

Use the UNION ALL operator to return all rows from multiple queries.

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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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;

…

Using the UNION ALL Operator

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 employee_id, job_id,department_id

FROM employees

UNION

SELECT employee_id, job_id,department_id

FROM job_history

ORDER BY 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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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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INTERSECT Operator

A B

The INTERSECT operator returns rows that are common to both queries.

INTERSECT Operator

Use the INTERSECT operator to return all rows that are common to multiple queries.

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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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;

Using the INTERSECT Operator

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;

Employee 200 is no longer part of the results because the EMPLOYEES.DEPARTMENT_ID value is

different from the JOB_HISTORY.DEPARTMENT_ID value.

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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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MINUS Operator

A B

The MINUS operator returns all the distinct rows selected by the first

query, but not present in the second query result set.

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).

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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Using the MINUS Operator

Display the employee IDs of those employees who have not

changed their jobs even once.

SELECT employee_id

FROM employees

MINUS

SELECT employee_id

FROM job_history;

…

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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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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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;

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.

The output of the query is shown:

…

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Oracle Database 11g: SQL Fundamentals I 8 - 26

Matching the SELECT Statement: Example

Using the UNION operator, display the employee ID, job ID, and

salary of all employees.

SELECT employee_id, job_id,salary

FROM employees

UNION

SELECT employee_id, job_id,0

FROM job_history;

…

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?

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 0is 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 0in the SALARY column.

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Oracle Database 11g: SQL Fundamentals I 8 - 27

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 - 28

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.

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.

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;

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 - 29

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.

Answer: 1, 3

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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

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 - 31

Practice 8: Overview

In this practice, you create reports by using:

•The UNION operator

•The INTERSECTION operator

•The MINUS operator

Practice 8: Overview

In this practice, you write queries using the set operators.

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Oracle Database 11g: SQL Fundamentals I 8 - 32

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.

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.

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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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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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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