Oracle Database Application Developer’s Guide Fundamentals Developer 10g Release 2

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Contents
Preface
What's New in Application Development?
Part I SQL for Application Developers
Part II PL/SQL for Application Developers
Part III Advanced Topics for Application Developers
Index
- Symbols
- A
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- C
- D
- E
- F
- G
- H
- I
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- K
- L
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Oracle® Database

Application Developer's Guide - Fundamentals

10g Release 2 (10.2)

B14251-01

November 2005

Oracle Database Application Developer’s Guide - Fundamentals, 10g Release 2 (10.2)

B14251-01

Primary Author: Lance Ashdown

Contributing Authors: D. Adams, M. Cowan, R. Moran, J. Melnick, E. Paapanen, J. Russell, R. Strohm

Contributors: D. Alpern, G. Arora, C. Barclay, D. Bronnikov, T. Chang, M. Davidson, G. Doherty, D. Elson,

A. Ganesh, M. Hartstein, J. Huang, N. Jain, R. Jenkins Jr., S. Kotsovolos, S. Kumar, C. Lei, D. Lorentz, V.

Moore, J. Muller, R. Murthy, R. Pang, B. Sinha, S. Vemuri, W. Wang, D. Wong, A. Yalamanchi, Q. Yu

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Contents

Preface ............................................................................................................................................................... xix

Audience..................................................................................................................................................... xix

Documentation Accessibility................................................................................................................... xix

Related Documents ................................................................................................................................... xx

Conventions ............................................................................................................................................... xxi

What's New in Application Development? ................................................................................ xxiii

Oracle Database 10g Release 2 (10.2) New Features........................................................................... xxiii

Oracle Database 10g Release 1 (10.1) New Features........................................................................... xxiv

1 Orientation to Oracle Programmatic Environments

Overview of Oracle Application Development ................................................................................. 1-1

Overview of PL/SQL................................................................................................................................ 1-2

What Is PL/SQL? ............................................................................................................................... 1-2

Advantages of PL/SQL..................................................................................................................... 1-3

Integration with Oracle Database............................................................................................. 1-4

High Performance....................................................................................................................... 1-4

High Productivity ....................................................................................................................... 1-4

Scalability ..................................................................................................................................... 1-4

Manageability.............................................................................................................................. 1-5

Object-Oriented Programming Support.................................................................................. 1-5

Portability..................................................................................................................................... 1-5

Security......................................................................................................................................... 1-5

Built-In Packages......................................................................................................................... 1-6

PL/SQL Web Development Tools................................................................................................... 1-6

Overview of Java Support Built Into the Database ........................................................................... 1-6

Overview of Oracle JVM................................................................................................................... 1-7

Overview of Oracle Extensions to JDBC......................................................................................... 1-8

JDBC Thin Driver........................................................................................................................ 1-8

JDBC OCI Driver......................................................................................................................... 1-8

JDBC Server-Side Internal Driver............................................................................................. 1-9

Oracle Database Extensions to JDBC Standards .................................................................... 1-9

Sample JDBC 2.0 Program ......................................................................................................... 1-9

Sample Pre-2.0 JDBC Program............................................................................................... 1-10

JDBC in SQLJ Applications..................................................................................................... 1-10

Overview of Oracle SQLJ............................................................................................................... 1-11

Benefits of SQLJ........................................................................................................................ 1-12

Comparing SQLJ with JDBC .................................................................................................. 1-12

SQLJ Stored Procedures in the Server................................................................................... 1-13

Overview of Oracle JPublisher...................................................................................................... 1-13

Overview of Java Stored Procedures............................................................................................ 1-13

Overview of Oracle Database Web Services ............................................................................... 1-14

Oracle Database as a Web Service Provider ........................................................................ 1-14

Overview of Writing Procedures and Functions in Java........................................................... 1-15

Overview of Writing Database Triggers in Java ................................................................. 1-15

Why Use Java for Stored Procedures and Triggers?........................................................... 1-15

Overview of Pro*C/C++ ....................................................................................................................... 1-15

Implementing a Pro*C/C++ Application.................................................................................... 1-16

Highlights of Pro*C/C++ Features............................................................................................... 1-17

Overview of Pro*COBOL .................................................................................................................... 1-18

How You Implement a Pro*COBOL Application ...................................................................... 1-18

Highlights of Pro*COBOL Features ............................................................................................. 1-19

Overview of OCI and OCCI................................................................................................................ 1-19

Advantages of OCI.......................................................................................................................... 1-20

Parts of the OCI ............................................................................................................................... 1-20

Procedural and Non-Procedural Elements ................................................................................. 1-21

Building an OCI Application......................................................................................................... 1-21

Overview of Oracle Data Provider for .NET (ODP.NET) .............................................................. 1-22

Using ODP.NET in a Simple Application ................................................................................... 1-22

Overview of Oracle Objects for OLE (OO4O)................................................................................. 1-23

OO4O Automation Server ............................................................................................................. 1-24

OO4O Object Model ....................................................................................................................... 1-25

OraSession................................................................................................................................. 1-25

OraServer .................................................................................................................................. 1-25

OraDatabase.............................................................................................................................. 1-26

OraDynaset ............................................................................................................................... 1-26

OraField..................................................................................................................................... 1-26

OraMetaData and OraMDAttribute...................................................................................... 1-27

OraParameters and OraParameter........................................................................................ 1-27

OraParamArray........................................................................................................................ 1-27

OraSQLStmt.............................................................................................................................. 1-27

OraAQ ....................................................................................................................................... 1-27

OraAQMsg................................................................................................................................ 1-28

OraAQAgent............................................................................................................................. 1-28

Support for Oracle LOB and Object Datatypes........................................................................... 1-28

OraBLOB and OraCLOB......................................................................................................... 1-29

OraBFILE................................................................................................................................... 1-29

Oracle Data Control........................................................................................................................ 1-29

Oracle Objects for OLE C++ Class Library.................................................................................. 1-29

Additional Sources of Information............................................................................................... 1-29

Choosing a Programming Environment ........................................................................................... 1-30

Choosing Whether to Use OCI or a Precompiler ....................................................................... 1-30

Using Built-In Packages and Libraries......................................................................................... 1-30

Java Compared to PL/SQL............................................................................................................ 1-31

PL/SQL Is Optimized for Database Access ......................................................................... 1-31

PL/SQL Is Integrated with the Database............................................................................. 1-31

Both Java and PL/SQL Have Object-Oriented Features.................................................... 1-31

Java Is Used for Open Distributed Applications................................................................. 1-32

Part I SQL for Application Developers

2 SQL Processing for Application Developers

Grouping Operations into Transactions .............................................................................................. 2-1

Deciding How to Group Operations in Transactions................................................................... 2-1

Improving Transaction Performance ............................................................................................. 2-2

Committing Transactions.................................................................................................................. 2-2

Managing Commit Redo Behavior........................................................................................... 2-3

Rolling Back Transactions ................................................................................................................ 2-4

Defining Transaction Savepoints .................................................................................................... 2-5

An Example of COMMIT, SAVEPOINT, and ROLLBACK ................................................. 2-5

Ensuring Repeatable Reads with Read-Only Transactions ............................................................ 2-5

Using Cursors within Applications ...................................................................................................... 2-6

Declaring and Opening Cursors ..................................................................................................... 2-6

Using a Cursor to Execute Statements Again ................................................................................ 2-7

Closing Cursors ................................................................................................................................. 2-7

Cancelling Cursors ............................................................................................................................ 2-8

Locking Data Explicitly .......................................................................................................................... 2-8

Choosing a Locking Strategy ........................................................................................................... 2-9

When to Lock with ROW SHARE and ROW EXCLUSIVE Mode....................................... 2-9

When to Lock with SHARE Mode............................................................................................ 2-9

When to Lock with SHARE ROW EXCLUSIVE Mode....................................................... 2-10

When to Lock in EXCLUSIVE Mode..................................................................................... 2-11

Privileges Required ................................................................................................................. 2-11

Letting Oracle Database Control Table Locking......................................................................... 2-11

Explicitly Acquiring Row Locks .................................................................................................. 2-12

About User Locks .................................................................................................................................. 2-13

When to Use User Locks ................................................................................................................ 2-13

Example of a User Lock.................................................................................................................. 2-13

Viewing and Monitoring Locks .................................................................................................... 2-14

Using Serializable Transactions for Concurrency Control ........................................................... 2-14

How Serializable Transactions Interact ....................................................................................... 2-15

Setting the Isolation Level of a Transaction ................................................................................ 2-16

The INITRANS Parameter ..................................................................................................... 2-16

Referential Integrity and Serializable Transactions .................................................................. 2-17

Using SELECT FOR UPDATE................................................................................................ 2-18

READ COMMITTED and SERIALIZABLE Isolation ............................................................... 2-18

Transaction Set Consistency .................................................................................................. 2-18

Comparison of READ COMMITTED and SERIALIZABLE Transactions....................... 2-19

Choosing an Isolation Level for Transactions...................................................................... 2-20

Application Tips for Transactions ................................................................................................ 2-20

Autonomous Transactions ................................................................................................................... 2-20

Examples of Autonomous Transactions...................................................................................... 2-22

Entering a Buy Order .............................................................................................................. 2-23

Example: Making a Bank Withdrawal.................................................................................. 2-23

Defining Autonomous Transactions ............................................................................................ 2-26

Restrictions on Autonomous Transactions.................................................................................. 2-27

Resuming Execution After a Storage Error Condition................................................................... 2-27

What Operations Can Be Resumed After an Error Condition?................................................ 2-27

Limitations on Resuming Operations After an Error Condition ............................................. 2-27

Writing an Application to Handle Suspended Storage Allocation.......................................... 2-28

Example of Resumable Storage Allocation ................................................................................. 2-28

3 Using SQL Datatypes in Application Development

Representing Data with SQL Datatypes: Overview.......................................................................... 3-1

Representing Character Data ................................................................................................................. 3-2

Representing Character Data: Overview........................................................................................ 3-2

Specifying Column Lengths as Bytes or Characters ..................................................................... 3-3

Choosing Between the CHAR and VARCHAR2 Datatypes........................................................ 3-3

Using Character Literals in SQL Statements.................................................................................. 3-4

Quoting Character Literals........................................................................................................ 3-5

Representing Numeric Data................................................................................................................... 3-5

What Are the Numeric Datatypes? ................................................................................................. 3-5

Using Floating-Point Number Formats .......................................................................................... 3-6

Using a Floating-Point Binary Format..................................................................................... 3-7

Representing Special Values with Native Floating-Point Formats ..................................... 3-8

Using Comparison Operators for Native Floating-Point Datatypes.......................................... 3-9

Performing Arithmetic Operations with Native Floating-Point Datatypes ........................... 3-10

Using Conversion Functions with Native Floating-Point Datatypes...................................... 3-10

Client Interfaces for Native Floating-Point Datatypes .............................................................. 3-11

OCI Native Floating-Point Datatypes SQLT_BFLOAT and SQLT_BDOUBLE.............. 3-11

Native Floating-Point Datatypes Supported in Oracle OBJECT Types........................... 3-12

Pro*C/C++ Support for Native Floating-Point Datatypes................................................ 3-12

Representing Datetime Data............................................................................................................... 3-12

Representing Datetime Data: Overview...................................................................................... 3-12

Using the DATE Datatype...................................................................................................... 3-12

Using the TIMESTAMP Datatype ......................................................................................... 3-12

Using the TIMESTAMP WITH TIME ZONE Datatype...................................................... 3-12

Using the TIMESTAMP WITH LOCAL TIME ZONE Datatype....................................... 3-13

Representing the Difference Between Datetime Values..................................................... 3-13

Manipulating the Date Format ..................................................................................................... 3-13

Changing the Default Date Format ....................................................................................... 3-13

Displaying the Current Date and Time ................................................................................ 3-14

Manipulating the Time Format .................................................................................................... 3-14

Performing Date Arithmetic.......................................................................................................... 3-14

Converting Between Datetime Types .......................................................................................... 3-15

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Importing and Exporting Datetime Types .................................................................................. 3-15

Representing Specialized Data........................................................................................................... 3-16

Representing Geographic Data ..................................................................................................... 3-16

Representing Multimedia Data..................................................................................................... 3-16

Representing Large Amounts of Data.......................................................................................... 3-16

Using RAW and LONG RAW Datatypes............................................................................. 3-17

Representing Searchable Text ....................................................................................................... 3-18

Representing XML .......................................................................................................................... 3-18

Representing Dynamically Typed Data....................................................................................... 3-19

Representing Data with ANSI/ISO, DB2, and SQL/DS Datatypes ....................................... 3-21

Representing Conditional Expressions as Data .............................................................................. 3-22

Identifying Rows by Address ............................................................................................................ 3-23

Querying the ROWID Pseudocolumn ......................................................................................... 3-24

Accessing the ROWID Datatype................................................................................................... 3-24

Restricted ROWID ................................................................................................................... 3-24

Extended ROWID .................................................................................................................... 3-24

External Binary ROWID.......................................................................................................... 3-25

Accessing the UROWID Datatype................................................................................................ 3-25

How Oracle Database Converts Datatypes ..................................................................................... 3-25

Datatype Conversion During Assignments................................................................................ 3-25

Datatype Conversion During Expression Evaluation .............................................................. 3-26

4 Using Regular Expressions in Oracle Database

Using Regular Expressions with Oracle Database: Overview ........................................................ 4-1

What Are Regular Expressions?....................................................................................................... 4-1

How Are Oracle Database Regular Expressions Useful?............................................................. 4-2

Oracle Database Implementation of Regular Expressions........................................................... 4-2

Oracle Database Support for the POSIX Regular Expression Standard..................................... 4-3

Regular Expression Metacharacters in Oracle Database .................................................................. 4-4

POSIX Metacharacters in Oracle Database Regular Expressions................................................ 4-4

Regular Expression Operator Multilingual Enhancements......................................................... 4-6

Perl-Influenced Extensions in Oracle Regular Expressions......................................................... 4-7

Using Regular Expressions in SQL Statements: Scenarios .............................................................. 4-9

Using an Integrity Constraint to Enforce a Phone Number Format........................................... 4-9

Using Back References to Reposition Characters....................................................................... 4-10

5 Using Indexes in Application Development

Guidelines for Application-Specific Indexes ..................................................................................... 5-1

Create Indexes After Inserting Table Data .................................................................................... 5-2

Switch Your Temporary Tablespace to Avoid Space Problems Creating Indexes................... 5-2

Index the Correct Tables and Columns .......................................................................................... 5-2

Limit the Number of Indexes for Each Table................................................................................. 5-3

Choose the Order of Columns in Composite Indexes .................................................................. 5-3

Gather Statistics to Make Index Usage More Accurate ................................................................ 5-4

Drop Indexes That Are No Longer Required ............................................................................... 5-4

Privileges Required to Create an Index ......................................................................................... 5-5

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Creating Indexes: Basic Examples ........................................................................................................ 5-5

When to Use Domain Indexes ............................................................................................................... 5-6

When to Use Function-Based Indexes.................................................................................................. 5-6

Advantages of Function-Based Indexes.......................................................................................... 5-6

Examples of Function-Based Indexes.............................................................................................. 5-7

Example: Function-Based Index for Case-Insensitive Searches........................................... 5-8

Example: Precomputing Arithmetic Expressions with a Function-Based Index............... 5-8

Example: Function-Based Index for Language-Dependent Sorting.................................... 5-8

Restrictions for Function-Based Indexes......................................................................................... 5-8

6 Maintaining Data Integrity in Application Development

Overview of Integrity Constraints........................................................................................................ 6-1

When to Enforce Business Rules with Integrity Constraints ...................................................... 6-1

Example of an Integrity Constraint for a Business Rule ....................................................... 6-2

When to Enforce Business Rules in Applications ......................................................................... 6-2

Creating Indexes for Use with Constraints .................................................................................... 6-2

When to Use NOT NULL Integrity Constraints ........................................................................... 6-2

When to Use Default Column Values ............................................................................................ 6-3

Setting Default Column Values ....................................................................................................... 6-4

Choosing a Table's Primary Key ..................................................................................................... 6-4

When to Use UNIQUE Key Integrity Constraints ........................................................................ 6-5

Constraints On Views: for Performance, Not Data Integrity....................................................... 6-5

Enforcing Referential Integrity with Constraints.............................................................................. 6-6

About Nulls and Foreign Keys......................................................................................................... 6-7

Defining Relationships Between Parent and Child Tables .......................................................... 6-8

Rules for Multiple FOREIGN KEY Constraints ............................................................................ 6-9

Deferring Constraint Checks............................................................................................................ 6-9

Guidelines for Deferring Constraint Checks .......................................................................... 6-9

Managing Constraints That Have Associated Indexes .................................................................. 6-10

Minimizing Space and Time Overhead for Indexes Associated with Constraints................ 6-10

Guidelines for Indexing Foreign Keys.............................................................................................. 6-11

About Referential Integrity in a Distributed Database................................................................. 6-11

When to Use CHECK Integrity Constraints..................................................................................... 6-11

Restrictions on CHECK Constraints ............................................................................................ 6-12

Designing CHECK Constraints .................................................................................................... 6-12

Rules for Multiple CHECK Constraints ...................................................................................... 6-12

Choosing Between CHECK and NOT NULL Integrity Constraints ...................................... 6-13

Examples of Defining Integrity Constraints ................................................................................... 6-13

Example: Defining Integrity Constraints with the CREATE TABLE Command .................. 6-13

Example: Defining Constraints with the ALTER TABLE Command...................................... 6-14

Privileges Required to Create Constraints ................................................................................. 6-14

Naming Integrity Constraints ...................................................................................................... 6-14

Enabling and Disabling Integrity Constraints ............................................................................... 6-14

Why Disable Constraints? ............................................................................................................. 6-15

About Exceptions to Integrity Constraints.................................................................................. 6-15

Enabling Constraints ..................................................................................................................... 6-15

Creating Disabled Constraints ..................................................................................................... 6-16

Enabling and Disabling Existing Integrity Constraints............................................................. 6-16

Enabling Existing Constraints ............................................................................................... 6-16

Disabling Existing Constraints .............................................................................................. 6-16

Tip: Using the Data Dictionary to Find Constraints........................................................... 6-17

Guidelines for Enabling and Disabling Key Integrity Constraints.......................................... 6-17

Fixing Constraint Exceptions ....................................................................................................... 6-17

Altering Integrity Constraints ............................................................................................................ 6-17

Renaming Integrity Constraints.................................................................................................... 6-18

Dropping Integrity Constraints.......................................................................................................... 6-19

Managing FOREIGN KEY Integrity Constraints ........................................................................... 6-19

Datatypes and Names for Foreign Key Columns....................................................................... 6-19

Limit on Columns in Composite Foreign Keys .......................................................................... 6-19

Foreign Key References Primary Key by Default....................................................................... 6-20

Privileges Required to Create FOREIGN KEY Integrity Constraints...................................... 6-20

Choosing How Foreign Keys Enforce Referential Integrity .................................................... 6-20

Viewing Definitions of Integrity Constraints ................................................................................ 6-21

Examples of Defining Integrity Constraints................................................................................ 6-21

Part II PL/SQL for Application Developers

7 Coding PL/SQL Procedures and Packages

Overview of PL/SQL Program Units ................................................................................................... 7-1

Anonymous Blocks ........................................................................................................................... 7-2

Stored Program Units (Procedures, Functions, and Packages) .................................................. 7-3

Naming Procedures and Functions ......................................................................................... 7-4

Parameters for Procedures and Functions ............................................................................. 7-4

Creating Stored Procedures and Functions ........................................................................... 7-7

Altering Stored Procedures and Functions ............................................................................ 7-8

Dropping Procedures and Functions ...................................................................................... 7-8

External Procedures ................................................................................................................... 7-9

PL/SQL Packages ...................................................................................................................... 7-9

PL/SQL Object Size Limitation ............................................................................................ 7-11

Creating Packages ................................................................................................................... 7-11

Naming Packages and Package Objects .............................................................................. 7-12

Package Invalidations and Session State ............................................................................. 7-12

Packages Supplied With Oracle Database ........................................................................... 7-12

Overview of Bulk Binds.......................................................................................................... 7-12

When to Use Bulk Binds ......................................................................................................... 7-13

Triggers ..................................................................................................................................... 7-15

Compiling PL/SQL Procedures for Native Execution .................................................................... 7-15

Remote Dependencies ......................................................................................................................... 7-15

Timestamps ..................................................................................................................................... 7-16

Disadvantages of the Timestamp Model ............................................................................. 7-16

Signatures ........................................................................................................................................ 7-16

When Does a Signature Change?........................................................................................... 7-18

Examples of Changing Procedure Signatures .................................................................... 7-19

Controlling Remote Dependencies .............................................................................................. 7-20

Dependency Resolution ......................................................................................................... 7-21

Suggestions for Managing Dependencies ........................................................................... 7-22

Cursor Variables ................................................................................................................................... 7-22

Declaring and Opening Cursor Variables .................................................................................. 7-22

Examples of Cursor Variables ...................................................................................................... 7-23

Fetching Data ........................................................................................................................... 7-23

Implementing Variant Records ............................................................................................. 7-24

Handling PL/SQL Compile-Time Errors ......................................................................................... 7-24

Handling Run-Time PL/SQL Errors .................................................................................................. 7-26

Declaring Exceptions and Exception Handling Routines ........................................................ 7-27

Unhandled Exceptions .................................................................................................................. 7-28

Handling Errors in Distributed Queries ..................................................................................... 7-28

Handling Errors in Remote Procedures ...................................................................................... 7-28

Debugging Stored Procedures............................................................................................................ 7-29

Calling Stored Procedures ................................................................................................................... 7-31

A Procedure or Trigger Calling Another Procedure.................................................................. 7-32

Interactively Calling Procedures From Oracle Database Tools ............................................... 7-32

Calling Procedures within 3GL Applications ............................................................................ 7-33

Name Resolution When Calling Procedures .............................................................................. 7-33

Privileges Required to Execute a Procedure .............................................................................. 7-33

Specifying Values for Procedure Arguments ............................................................................. 7-34

Calling Remote Procedures ................................................................................................................ 7-34

Remote Procedure Calls and Parameter Values......................................................................... 7-35

Referencing Remote Objects.......................................................................................................... 7-35

Synonyms for Procedures and Packages .................................................................................... 7-36

Calling Stored Functions from SQL Expressions ........................................................................... 7-36

Using PL/SQL Functions .............................................................................................................. 7-37

Syntax for SQL Calling a PL/SQL Function ............................................................................... 7-37

Naming Conventions ..................................................................................................................... 7-37

Name Precedence .................................................................................................................... 7-38

Arguments ............................................................................................................................... 7-39

Using Default Values .............................................................................................................. 7-39

Privileges .................................................................................................................................. 7-39

Requirements for Calling PL/SQL Functions from SQL Expressions .................................... 7-39

Controlling Side Effects ................................................................................................................. 7-40

Restrictions................................................................................................................................ 7-40

Declaring a Function ............................................................................................................... 7-41

Parallel Query and Parallel DML ......................................................................................... 7-42

PRAGMA RESTRICT_REFERENCES – for Backward Compatibility ............................. 7-43

Serially Reusable PL/SQL Packages ........................................................................................... 7-46

Package States .......................................................................................................................... 7-47

Why Serially Reusable Packages? ......................................................................................... 7-47

Syntax of Serially Reusable Packages ................................................................................... 7-47

Semantics of Serially Reusable Packages.............................................................................. 7-47

Examples of Serially Reusable Packages .............................................................................. 7-48

Returning Large Amounts of Data from a Function....................................................................... 7-51

Coding Your Own Aggregate Functions ........................................................................................... 7-52

8 Coding Dynamic SQL

What Is Dynamic SQL? ........................................................................................................................... 8-1

Programming with Dynamic SQL................................................................................................... 8-1

Why Use Dynamic SQL?......................................................................................................................... 8-2

Executing DDL and SCL Statements in PL/SQL .......................................................................... 8-3

Executing Dynamic Queries............................................................................................................. 8-4

Referencing Database Objects that Do Not Exist at Compilation............................................... 8-4

Optimizing Execution Dynamically ............................................................................................... 8-5

Executing Dynamic PL/SQL Blocks ............................................................................................... 8-5

Performing Dynamic Operations Using Invoker's Rights .......................................................... 8-6

Developing with Native Dynamic SQL: Scenario............................................................................. 8-7

Sample DML Operation Using Native Dynamic SQL.................................................................. 8-7

Sample DDL Operation Using Native Dynamic SQL................................................................... 8-8

Sample Single-Row Query Using Native Dynamic SQL.............................................................. 8-8

Sample Multiple-Row Query with Native Dynamic SQL............................................................ 8-9

Choosing Between Native Dynamic SQL and the DBMS_SQL Package ..................................... 8-9

Advantages of Native Dynamic SQL........................................................................................... 8-10

Native Dynamic SQL is Easy to Use ..................................................................................... 8-10

Native Dynamic SQL is Faster than DBMS_SQL................................................................ 8-11

Native Dynamic SQL Supports User-Defined Types......................................................... 8-12

Native Dynamic SQL Supports Fetching into Records...................................................... 8-12

Advantages of the DBMS_SQL Package...................................................................................... 8-13

DBMS_SQL is Supported in Client-Side Programs ............................................................ 8-13

DBMS_SQL Supports Statements with Unknown Number of Inputs or Outputs ........ 8-13

DBMS_SQL Supports SQL Statements Larger than 32 KB ................................................ 8-13

DBMS_SQL Lets You Reuse SQL Statements...................................................................... 8-13

Examples of DBMS_SQL Package Code and Native Dynamic SQL Code............................. 8-14

Querying with Dynamic SQL: Example............................................................................... 8-14

Performing DML with Dynamic SQL: Example ................................................................. 8-15

Performing DML with RETURNING Clause Using Dynamic SQL: Example ............... 8-16

Avoiding SQL Injection in PL/SQL ................................................................................................... 8-17

Overview of SQL Injection Techniques ....................................................................................... 8-17

Statement Modification........................................................................................................... 8-18

Statement Injection .................................................................................................................. 8-19

Guarding Against SQL Injection................................................................................................... 8-21

Using Bind Variables to Guard Against SQL Injection ...................................................... 8-21

Using Validation Checks to Guard Against SQL Injection................................................ 8-22

9 Coding Triggers

Designing Triggers................................................................................................................................... 9-1

Creating Triggers ..................................................................................................................................... 9-2

Types of Triggers ............................................................................................................................... 9-3

Overview of System Events....................................................................................................... 9-3

Getting the Attributes of System Events ................................................................................. 9-3

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Naming Triggers ............................................................................................................................... 9-3

When Is the Trigger Fired? .............................................................................................................. 9-3

Do Import and SQL*Loader Fire Triggers?............................................................................. 9-4

How Column Lists Affect UPDATE Triggers ........................................................................ 9-4

Controlling When a Trigger Is Fired (BEFORE and AFTER Options) ...................................... 9-4

Ordering of Triggers ......................................................................................................................... 9-5

Modifying Complex Views (INSTEAD OF Triggers)................................................................... 9-6

Views that Require INSTEAD OF Triggers............................................................................. 9-6

INSTEAD OF Trigger Example................................................................................................. 9-7

Object Views and INSTEAD OF Triggers .............................................................................. 9-8

Triggers on Nested Table View Columns ............................................................................... 9-8

Firing Triggers One or Many Times (FOR EACH ROW Option) .............................................. 9-9

Firing Triggers Based on Conditions (WHEN Clause) ............................................................. 9-10

Coding the Trigger Body ..................................................................................................................... 9-10

Accessing Column Values in Row Triggers ............................................................................... 9-12

Example: Modifying LOB Columns with a Trigger............................................................ 9-12

INSTEAD OF Triggers on Nested Table View Columns ................................................... 9-13

Avoiding Name Conflicts with Triggers (REFERENCING Option) ............................... 9-13

Detecting the DML Operation That Fired a Trigger........................................................... 9-14

Error Conditions and Exceptions in the Trigger Body ...................................................... 9-14

Triggers on Object Tables............................................................................................................... 9-14

Triggers and Handling Remote Exceptions ............................................................................... 9-15

Restrictions on Creating Triggers ................................................................................................ 9-16

Who Is the Trigger User? ............................................................................................................... 9-19

Privileges Needed to Work with Triggers .................................................................................. 9-19

Compiling Triggers .............................................................................................................................. 9-20

Dependencies for Triggers ............................................................................................................ 9-20

Recompiling Triggers .................................................................................................................... 9-20

Modifying Triggers .............................................................................................................................. 9-21

Debugging Triggers ....................................................................................................................... 9-21

Enabling and Disabling Triggers ....................................................................................................... 9-21

Enabling Triggers ........................................................................................................................... 9-21

Disabling Triggers .......................................................................................................................... 9-21

Viewing Information About Triggers ............................................................................................... 9-22

Examples of Trigger Applications ..................................................................................................... 9-23

Responding to System Events through Triggers ............................................................................ 9-37

How Events Are Published Through Triggers ........................................................................... 9-37

Publication Context......................................................................................................................... 9-38

Error Handling ................................................................................................................................ 9-38

Execution Model.............................................................................................................................. 9-38

Event Attribute Functions.............................................................................................................. 9-38

List of Database Events .................................................................................................................. 9-41

System Events........................................................................................................................... 9-41

Client Events............................................................................................................................. 9-42

10 Developing Flashback Applications

Overview of Flashback Features ....................................................................................................... 10-1

xiii

Application Development Features.............................................................................................. 10-2

Database Administration Features............................................................................................... 10-2

Database Administration Tasks Before Using Flashback Features ............................................. 10-3

Using Flashback Query (SELECT ... AS OF) ................................................................................... 10-4

Examining Past Data: Example..................................................................................................... 10-5

Tips for Using Flashback Query ................................................................................................... 10-5

Using the DBMS_FLASHBACK Package......................................................................................... 10-6

Using ORA_ROWSCN......................................................................................................................... 10-7

Using Flashback Version Query ........................................................................................................ 10-8

Using Flashback Transaction Query................................................................................................ 10-10

Flashback Transaction Query and Flashback Version Query: Example............................... 10-10

Flashback Tips ..................................................................................................................................... 10-12

Flashback Tips – Performance..................................................................................................... 10-12

Flashback Tips – General ............................................................................................................. 10-13

11 Developing Applications with the PL/SQL Web Toolkit

Developing PL/SQL Web Applications: Overview ........................................................................ 11-1

Invoking a PL/SQL Web Application.......................................................................................... 11-1

Implementing a PL/SQL Web Application ................................................................................ 11-2

PL/SQL Web Toolkit............................................................................................................... 11-2

Using the mod_plsql Gateway ........................................................................................................... 11-3

Generating HTML Output with PL/SQL.......................................................................................... 11-4

Passing Parameters to a PL/SQL Web Application......................................................................... 11-5

Passing List and Dropdown List Parameters from an HTML Form ....................................... 11-5

Passing Radio Button and Checkbox Parameters from an HTML Form................................ 11-6

Passing Entry Field Parameters from an HTML Form.............................................................. 11-6

Passing Hidden Parameters from an HTML Form.................................................................... 11-8

Uploading a File from an HTML Form........................................................................................ 11-8

Submitting a Completed HTML Form......................................................................................... 11-8

Handling Missing Input from an HTML Form .......................................................................... 11-9

Maintaining State Information Between Web Pages ................................................................. 11-9

Performing Network Operations within PL/SQL Stored Procedures....................................... 11-10

Sending E-Mail from PL/SQL..................................................................................................... 11-10

Getting a Host Name or Address from PL/SQL...................................................................... 11-10

Working with TCP/IP Connections from PL/SQL ................................................................. 11-11

Retrieving the Contents of an HTTP URL from PL/SQL ....................................................... 11-11

Working with Tables, Image Maps, Cookies, and CGI Variables from PL/SQL ............... 11-13

12 Developing PL/SQL Server Pages

PL/SQL Server Pages: Overview ........................................................................................................ 12-1

What Are PL/SQL Server Pages and Why Use Them?............................................................. 12-1

Prerequisites for Developing and Deploying PL/SQL Server Pages...................................... 12-2

PSP and the HTP Package.............................................................................................................. 12-3

PSP and Other Scripting Solutions ............................................................................................... 12-3

Writing a PL/SQL Server Page ............................................................................................................ 12-4

Specifying Basic Server Page Characteristics.............................................................................. 12-5

xiv

Specifying the Scripting Language........................................................................................ 12-5

Returning Data to the Client .................................................................................................. 12-5

Handling Script Errors............................................................................................................ 12-7

Accepting User Input...................................................................................................................... 12-7

Naming the PL/SQL Stored Procedure....................................................................................... 12-8

Including the Contents of Other Files.......................................................................................... 12-8

Declaring Global Variables in a PSP Script ................................................................................. 12-9

Specifying Executable Statements in a PSP Script...................................................................... 12-9

Substituting an Expression Result in a PSP Script ................................................................... 12-10

Quoting and Escaping Strings in a PSP Script.......................................................................... 12-11

Including Comments in a PSP Script ......................................................................................... 12-11

Loading a PL/SQL Server Page into the Database ........................................................................ 12-12

Querying PSP Source Code ......................................................................................................... 12-13

Executing a PL/SQL Server Page Through a URL......................................................................... 12-14

Examples of PL/SQL Server Pages ................................................................................................... 12-15

Setup for PL/SQL Server Pages Examples................................................................................ 12-15

Printing the Sample Table with a Loop ..................................................................................... 12-16

Allowing a User Selection............................................................................................................ 12-17

Using an HTML Form to Call a PL/SQL Server Page............................................................. 12-18

Including JavaScript in a PSP File ....................................................................................... 12-19

Debugging PL/SQL Server Page Problems .................................................................................... 12-20

Putting PL/SQL Server Pages into Production .............................................................................. 12-21

13 Developing Applications with Database Change Notification

What Is Database Change Notification?........................................................................................... 13-1

Using Database Change Notification in the Middle Tier ............................................................. 13-2

Registering Queries for Database Change Notification................................................................ 13-5

Privileges .......................................................................................................................................... 13-5

What Is a Database Change Registration?................................................................................... 13-5

Supported Query Types................................................................................................................. 13-6

Registration Properties................................................................................................................... 13-6

Drop Table........................................................................................................................................ 13-7

Interfaces for Database Change Registration.............................................................................. 13-8

Creating a PL/SQL Stored Procedure as the Change Notification Recipient........................ 13-8

Registering Queries for Change Notification Through PL/SQL ............................................. 13-9

Creating a CHNF$_REG_INFO Object................................................................................. 13-9

Creating a Registration with DBMS_CHANGE_NOTIFICATION................................ 13-11

Adding Objects to an Existing Registration....................................................................... 13-12

Querying Change Notification Registrations................................................................................ 13-12

Interpreting a Database Change Notification................................................................................ 13-13

Interpreting a CHNF$_DESC Object.......................................................................................... 13-13

Interpreting a CHNF$_TDESC Object ................................................................................ 13-13

Interpreting a CHNF$_RDESC Object................................................................................ 13-14

Configuring Database Change Notification: Scenario ................................................................ 13-14

Creating a PL/SQL Callback Procedure.................................................................................... 13-15

Registering the Query................................................................................................................... 13-16

Best Practices ........................................................................................................................................ 13-17

Troubleshooting................................................................................................................................... 13-18

Part III Advanced Topics for Application Developers

14 Calling External Procedures

Overview of Multi-Language Programs ........................................................................................... 14-1

What Is an External Procedure? .......................................................................................................... 14-2

Overview of The Call Specification for External Procedures....................................................... 14-3

Loading External Procedures .............................................................................................................. 14-3

Loading Java Class Methods ......................................................................................................... 14-3

Loading External C Procedures .................................................................................................... 14-4

Publishing External Procedures ......................................................................................................... 14-8

The AS LANGUAGE Clause for Java Class Methods ............................................................... 14-9

The AS LANGUAGE Clause for External C Procedures .......................................................... 14-9

LIBRARY .................................................................................................................................. 14-9

NAME ..................................................................................................................................... 14-10

LANGUAGE .......................................................................................................................... 14-10

CALLING STANDARD ....................................................................................................... 14-10

WITH CONTEXT .................................................................................................................. 14-10

PARAMETERS ...................................................................................................................... 14-10

AGENT IN .............................................................................................................................. 14-10

Publishing Java Class Methods........................................................................................................ 14-10

Publishing External C Procedures ................................................................................................... 14-11

Locations of Call Specifications ....................................................................................................... 14-11

Passing Parameters to External C Procedures with Call Specifications ................................... 14-14

Specifying Datatypes .................................................................................................................... 14-15

External Datatype Mappings....................................................................................................... 14-16

BY VALUE/REFERENCE for IN and IN OUT Parameter Modes ....................................... 14-18

The PARAMETERS Clause.......................................................................................................... 14-18

Overriding Default Datatype Mapping..................................................................................... 14-19

Specifying Properties.................................................................................................................... 14-19

INDICATOR ........................................................................................................................... 14-20

LENGTH and MAXLEN....................................................................................................... 14-21

CHARSETID and CHARSETFORM.................................................................................... 14-21

Repositioning Parameters..................................................................................................... 14-22

Using SELF.............................................................................................................................. 14-22

Passing Parameters by Reference ........................................................................................ 14-24

WITH CONTEXT................................................................................................................... 14-25

Inter-Language Parameter Mode Mappings...................................................................... 14-25

Executing External Procedures with the CALL Statement .......................................................... 14-25

Preconditions for External Procedures ...................................................................................... 14-26

Privileges of External Procedures........................................................................................ 14-26

Managing Permissions.......................................................................................................... 14-27

Creating Synonyms for External Procedures..................................................................... 14-27

CALL Statement Syntax............................................................................................................... 14-27

Calling Java Class Methods ......................................................................................................... 14-28

xvi

How the Database Server Calls External C Procedures .......................................................... 14-28

Handling Errors and Exceptions in Multi-Language Programs................................................. 14-29

Using Service Procedures with External C Procedures................................................................ 14-29

Doing Callbacks with External C Procedures................................................................................ 14-35

Object Support for OCI Callbacks............................................................................................... 14-37

Restrictions on Callbacks ............................................................................................................. 14-37

Debugging External Procedures ................................................................................................. 14-38

Using Package DEBUG_EXTPROC .................................................................................... 14-38

Demo Program .............................................................................................................................. 14-39

Guidelines for External C Procedures........................................................................................ 14-39

Restrictions on External C Procedures....................................................................................... 14-40

15 Developing Applications with Oracle XA

X/Open Distributed Transaction Processing (DTP)........................................................................ 15-1

DTP Terminology............................................................................................................................ 15-2

Required Public Information......................................................................................................... 15-4

Oracle XA Library Interface Subroutines......................................................................................... 15-4

XA Library Subroutines ................................................................................................................. 15-5

Extensions to the XA Interface ...................................................................................................... 15-5

Developing and Installing XA Applications ................................................................................... 15-6

Responsibilities of the DBA or System Administrator .............................................................. 15-6

Responsibilities of the Application Developer ........................................................................... 15-7

Defining the xa_open() String ....................................................................................................... 15-7

Syntax of the xa_open() String ............................................................................................... 15-7

Required Fields for the xa_open() String.............................................................................. 15-8

Optional Fields for the xa_open() String .............................................................................. 15-8

Interfacing XA with Precompilers and OCI.............................................................................. 15-10

Using Precompilers with the Oracle XA Library .............................................................. 15-10

Using OCI with the Oracle XA Library .............................................................................. 15-11

Managing Transaction Control with XA ................................................................................... 15-12

Examples of Precompiler Applications .............................................................................. 15-13

Migrating Precompiler or OCI Applications to TPM Applications....................................... 15-14

Managing XA Library Thread Safety......................................................................................... 15-15

Specifying Threading in the Open String........................................................................... 15-15

Restrictions on Threading in XA ......................................................................................... 15-15

Troubleshooting XA Applications ................................................................................................... 15-15

Accessing XA Trace Files ............................................................................................................. 15-16

The xa_open() String DbgFl.................................................................................................. 15-16

Trace File Locations ............................................................................................................... 15-17

Managing In-Doubt or Pending Transactions .......................................................................... 15-17

Using SYS Account Tables to Monitor XA Transactions......................................................... 15-17

XA Issues and Restrictions ................................................................................................................ 15-18

Using Database Links in XA Applications................................................................................ 15-18

Managing Transaction Branches in XA Applications.............................................................. 15-19

Using XA with Oracle Real Application Clusters .................................................................... 15-19

Managing Transaction Branches on Oracle Real Application Clusters (RAC)............. 15-19

Managing Instance Recovery in Real Application Clusters ............................................ 15-20

xvii

Global Uniqueness of XIDs in Real Application Clusters................................................ 15-21

SQL-Based XA Restrictions.......................................................................................................... 15-21

Rollbacks and Commits ........................................................................................................ 15-21

DDL Statements ..................................................................................................................... 15-22

Session State............................................................................................................................ 15-22

EXEC SQL ............................................................................................................................... 15-22

Miscellaneous Restrictions........................................................................................................... 15-22

16 Developing Applications on the Publish-Subscribe Model

Introduction to Publish-Subscribe .................................................................................................... 16-1

Publish-Subscribe Architecture ......................................................................................................... 16-2

Publish-Subscribe Concepts ............................................................................................................... 16-3

Examples of a Publish-Subscribe Mechanism ................................................................................ 16-5

Index

xviii

xix

Preface

The Oracle Database Application Developer's Guide - Fundamentals describes basic

application development features of Oracle Database 10g. Information in this guide

applies to features that work the same on all supported platforms, and does not

include system-specific information.

Audience

Oracle Database Application Developer's Guide - Fundamentals is intended for

programmers developing new applications or converting existing applications to run

in the Oracle Database environment. This book will also be valuable to systems

analysts, project managers, and others interested in the development of database

applications.

To use this document, you need a working knowledge of application programming,

and that you are acquainted with using the Structured Query Language (SQL) to

access information in relational database systems. Some sections of this guide assume

a familiar with object-oriented programming.

Documentation Accessibility

Our goal is to make Oracle products, services, and supporting documentation

accessible, with good usability, to the disabled community. To that end, our

documentation includes features that make information available to users of assistive

technology. This documentation is available in HTML format, and contains markup to

facilitate access by the disabled community. Accessibility standards will continue to

evolve over time, and Oracle is actively engaged with other market-leading

technology vendors to address technical obstacles so that our documentation can be

accessible to all of our customers. For more information, visit the Oracle Accessibility

Program Web site at

http://www.oracle.com/accessibility/

Accessibility of Code Examples in Documentation

Screen readers may not always correctly read the code examples in this document. The

conventions for writing code require that closing braces should appear on an

otherwise empty line; however, some screen readers may not always read a line of text

that consists solely of a bracket or brace.

Accessibility of Links to External Web Sites in Documentation

This documentation may contain links to Web sites of other companies or

organizations that Oracle does not own or control. Oracle neither evaluates nor makes

any representations regarding the accessibility of these Web sites.

TTY Access to Oracle Support Services

Oracle provides dedicated Text Telephone (TTY) access to Oracle Support Services

within the United States of America 24 hours a day, seven days a week. For TTY

support, call 800.446.2398.

See Also:

■Oracle Database PL/SQL User's Guide and Reference

■Oracle Database SQL Reference

Overview of PL/SQL

1-4 Oracle Database Application Developer’s Guide - Fundamentals

■Scalability

■Manageability

■Object-Oriented Programming Support

■Portability

■Security

■Built-In Packages

Integration with Oracle Database

PL/SQL enables you use all of the Oracle Database SQL data manipulation, cursor

control, and transaction control statements. PL/SQL also supports the SQL functions,

operators, and pseudocolumns. So, you can manipulate data in Oracle Database

flexibly and safely.

PL/SQL supports all SQL datatypes. Combined with the direct access that SQL

provides, these shared datatypes integrate PL/SQL with the Oracle Database data

dictionary.

PL/SQL supports Dynamic SQL, which is a programming technique that enables you

to build and process SQL statements "on the fly" at run time. It gives PL/SQL

flexibility comparable to scripting languages such as Perl, Korn shell, and Tcl.

The %TYPE and %ROWTYPE attributes enable your code to adapt as table definitions

change. For example, the %TYPE attribute declares a variable based on the type of a

database column. If the column datatype changes, then the variable uses the correct

type at runtime. This provides data independence and reduces maintenance costs.

High Performance

If your application is database intensive, then you can use PL/SQL blocks to group

SQL statements before sending them to Oracle Database for execution. This coding

strategy can drastically reduce the communication overhead between your application

and Oracle Database.

PL/SQL stored procedures are compiled once and stored in executable form, so

procedure calls are quick and efficient. A single call can start a compute-intensive

stored procedure, reducing network traffic and improving round-trip response times.

Executable code is automatically cached and shared among users, lowering memory

requirements and invocation overhead.

High Productivity

PL/SQL adds procedural capabilities such as Oracle Forms and Oracle Reports. For

example, you can use an entire PL/SQL block in an Oracle Forms trigger instead of

multiple trigger steps, macros, or user exits.

PL/SQL is the same in all environments. As soon as you master PL/SQL with one

Oracle tool, you can transfer your knowledge to others, and so multiply the

productivity gains. For example, scripts written with one tool can be used by other

tools.

Scalability

PL/SQL stored procedures increase scalability by centralizing application processing

on the server. Automatic dependency tracking helps you develop scalable

applications.

Overview of PL/SQL

Orientation to Oracle Programmatic Environments 1-5

The shared memory facilities of the shared server enable Oracle Database to support

many thousands of concurrent users on a single node. For more scalability, you can

use the Oracle Connection Manager to multiplex network connections.

Manageability

After being validated, you can use a PL/SQL stored procedure in any number of

applications. If its definition changes, then only the procedure is affected, not the

applications that call it. This simplifies maintenance and enhancement. Also,

maintaining a procedure on the Oracle Database is easier than maintaining copies on

various client machines.

Object-Oriented Programming Support

You can use PL/SQL object types and collections for object-oriented programming.

Object Types An object type is a user-defined composite datatype that encapsulates a

data structure along with the functions and procedures needed to manipulate the data.

The variables that form the data structure are called attributes. The functions and

procedures that characterize the behavior of the object type are called methods, which

you can implement in PL/SQL.

Object types are an ideal object-oriented modeling tool, which you can use to reduce

the cost and time required to build complex applications. Besides allowing you to

create software components that are modular, maintainable, and reusable, object types

allow different teams of programmers to develop software components concurrently.

Collections A collection is an ordered group of elements, all of the same type (for

example, the grades for a class of students). Each element has a unique subscript that

determines its position in the collection. PL/SQL offers two kinds of collections:

nested tables and varrays (variable-size arrays).

Collections work like the set, queue, stack, and hash table data structures found in

most third-generation programming languages. Collections can store instances of an

object type and can also be attributes of an object type. Collections can be passed as

parameters. So, you can use them to move columns of data into and out of database

tables or between client-side applications and stored subprograms. You can define

collection types in a PL/SQL package, then use the same types across many

applications.

Portability

Applications written in PL/SQL can run on any operating system and hardware

platform on which Oracle Database runs. You can write portable program libraries and

reuse them in different environments.

Security

PL/SQL stored procedures enable you to divide application logic between the client

and the server, which prevents client applications from manipulating sensitive Oracle

Database data. Database triggers written in PL/SQL can prevent applications from

making specified updates and can audit user queries.

You can restrict access to Oracle Database data by allowing users to manipulate it only

through stored procedures that have a restricted set of privileges. For example, you

can grant users access to a procedure that updates a table but not grant them access to

the table itself.

Overview of Java Support Built Into the Database

1-6 Oracle Database Application Developer’s Guide - Fundamentals

Built-In Packages

A package is an encapsulated collection of related program objects stored together in

the database. Program objects are procedures, functions, variables, constants, cursors,

and exceptions.

The following packages are especially useful in application development for Oracle

Database:

■DBMS_PIPE is used to communicate between sessions.

■DBMS_ALERT is used to broadcast alerts to users.

■DBMS_LOCK and DBMS_TRANSACTION are used for lock and transaction

management.

■DBMS_AQ is used for Advanced Queuing.

■DBMS_LOB is used to manipulate large objects.

■DBMS_ROWID is used for employing ROWID values.

■UTL_RAW is the RAW facility.

■UTL_REF is for work with REF values.

The following packages are useful for server manageability:

■DBMS_SESSION is for session management by DBAs.

■DBMS_SPACE and DBMS_SHARED_POOL provide space information and reserve

shared pool resources.

■DBMS_JOB is used to schedule jobs in the server.

PL/SQL Web Development Tools

Oracle Database provides built-in tools and technologies that enable you to deploy

PL/SQL applications over the Web. Thus, PL/SQL serves as an alternative to Web

application frameworks such as CGI.

The PL/SQL Web Toolkit is a set of PL/SQL packages that you can use to develop

stored procedures that can be invoked by a Web client. The PL/SQL Gateway enables

an HTTP client to invoke a PL/SQL stored procedure through mod_plsql, which is a

plug-in to Oracle HTTP Server. This module performs the following actions:

1. Translates a URL passed by a browser client

2. Calls an Oracle Database stored procedure with the parameters in the URL

3. Returns output (typically HTML) to the client

Overview of Java Support Built Into the Database

This section provides an overview of built-in database features that support Java

applications. The database includes the core JDK libraries such as java.lang,

java.io, and so on. The database supports client-side Java standards such as JDBC

See Also: Oracle Database Security Guide for details on database

security features

See Also: Chapter 11, "Developing Applications with the PL/SQL

Web Toolkit" to learn how to use PL/SQL in Web development

Overview of Java Support Built Into the Database

Orientation to Oracle Programmatic Environments 1-7

and SQLJ, and provides server-side JDBC and SQLJ drivers that allow data-intensive

Java code to run within the database.

This section contains the following topics:

■Overview of Oracle JVM

■Overview of Oracle Extensions to JDBC

■Overview of Oracle SQLJ

■Overview of Oracle JPublisher

■Overview of Java Stored Procedures

■Overview of Oracle Database Web Services

■Overview of Writing Procedures and Functions in Java

Overview of Oracle JVM

Oracle JVM, the Java Virtual Machine provided with the Oracle Database, is compliant

with the J2SE version 1.4.x specification and supports the database session

architecture.

Any database session can activate a dedicated JVM. All sessions share the same JVM

code and statics; however, private states for any given session are held, and

subsequently garbage collected, in an individual session space.

This design provides the following benefits:

■Java applications have the same session isolation and data integrity as SQL

operations.

■There is no need to run Java in a separate process for data integrity.

■Oracle JVM is a robust JVM with a small memory footprint.

■The JVM has the same linear Symmetric Multiprocessing (SMP) scalability as the

database and can support thousands of concurrent Java sessions.

Oracle JVM works consistently with every platform supported by Oracle Database.

Java applications that you develop with Oracle JVM can easily be ported to any

supported platform.

Oracle JVM includes a deployment-time native compiler that enables Java code to be

compiled once, stored in executable form, shared among users, and invoked more

quickly and efficiently.

Security features of the database are also available with Oracle JVM. Java classes must

be loaded in a database schema (by using Oracle JDeveloper, a third-party IDE,

SQL*Plus, or the loadjava utility) before they can be invoked. Java class invocation is

secured and controlled through database authentication and authorization, Java 2

security, and invoker's or definer's rights.

See Also:

■Oracle Database Concepts for background information about Java

and how the database supports it

■Oracle Database Java Developer's Guide

■Oracle Database JDBC Developer's Guide and Reference

■Oracle Database JPublisher User's Guide

Overview of Java Support Built Into the Database

1-8 Oracle Database Application Developer’s Guide - Fundamentals

Overview of Oracle Extensions to JDBC

JDBC (Java Database Connectivity) is an API (Applications Programming Interface)

that allows Java to send SQL statements to an object-relational database such as Oracle

Database.

The JDBC standard defines four types of JDBC drivers:

■Type 1. A JDBC-ODBC bridge. Software must be installed on client systems.

■Type 2. Native methods (calls C or C++) and Java methods. Software must be

installed on the client.

■Type 3. Pure Java. The client uses sockets to call middleware on the server.

■Type 4. The most pure Java solution. Talks directly to the database by using Java

sockets.

JDBC is based on the X/Open SQL Call Level Interface, and complies with the SQL92

Entry Level standard.

You can use JDBC to do dynamic SQL. In dynamic SQL, the embedded SQL statement

to be executed is not known before the application is run and requires input to build

the statement.

The drivers that are implemented by Oracle have extensions to the capabilities in the

JDBC standard that was defined by Sun Microsystems. Oracle's implementations of

JDBC drivers are described in the following sections. Oracle Database support of and

extensions to various levels of the JDBC standard are described in "Oracle Database

Extensions to JDBC Standards" on page 1-9.

JDBC Thin Driver

The JDBC thin driver is a Type 4 (100% pure Java) driver that uses Java sockets to

connect directly to a database server. It has its own implementation of a Two-Task

Common (TTC), a lightweight implementation of TCP/IP from Oracle Net. It is

written entirely in Java and is therefore platform-independent.

The thin driver does not require Oracle software on the client side. It does need a

TCP/IP listener on the server side. Use this driver in Java applets that are downloaded

into a Web browser or in applications for which you do not want to install Oracle

client software. The thin driver is self-contained, but it opens a Java socket, and thus

can only run in a browser that supports sockets.

JDBC OCI Driver

The OCI driver is a Type 2 JDBC driver. It makes calls to the OCI (Oracle Call

Interface) written in C to interact with Oracle Database, thus using native and Java

methods.

The OCI driver allows access to more features than the thin driver, such as Transparent

Application Fail-Over, advanced security, and advanced LOB manipulation.

The OCI driver provides the highest compatibility between different Oracle Database

versions. It also supports all installed Oracle Net adapters, including IPC, named

pipes, TCP/IP, and IPX/SPX.

Because it uses native methods (a combination of Java and C) the OCI driver is

platform-specific. It requires a client installation of version Oracle8i or later including

Oracle Net, OCI libraries, CORE libraries, and all other dependent files. The OCI

driver usually executes faster than the thin driver.

Overview of Java Support Built Into the Database

Orientation to Oracle Programmatic Environments 1-9

The OCI driver is not appropriate for Java applets, because it uses a C library that is

platform-specific and cannot be downloaded into a Web browser. It is usable in J2EE

components running in middle-tier application servers, such as Oracle Application

Server. Oracle Application Server provides middleware services and tools that support

access between applications and browsers.

JDBC Server-Side Internal Driver

The JDBC server-side internal driver is a Type 2 driver that runs inside the database

server, reducing the number of round-trips needed to access large amounts of data.

The driver, the Java server VM, the database, the Java native compiler which speeds

execution by as much as 10 times, and the SQL engine all run within the same address

space.

This driver provides server-side support for any Java program used in the database:

SQLJ stored procedures, functions, triggers, and Java stored procedures. You can also

call PL/SQL stored procedures, functions, and triggers.

The server driver fully supports the same features and extensions as the client-side

drivers.

Oracle Database Extensions to JDBC Standards

Oracle Database includes the following extensions to the JDBC 1.22 standard:

■Support for Oracle datatypes

■Performance enhancement by row prefetching

■Performance enhancement by execution batching

■Specification of query column types to save round-trips

■Control of DatabaseMetaData calls

Oracle Database supports all APIs from the JDBC 2.0 standard, including the core

APIs, optional packages, and numerous extensions. Some of the highlights include

datasources, JTA, and distributed transactions.

Oracle Database supports the following features from the JDBC 3.0 standard:

■Support for JDK 1.4.

■Toggling between local and global transactions.

■Transaction savepoints.

■Reuse of prepared statements by connection pools.

Sample JDBC 2.0 Program

The following example shows the recommended technique for looking up a data

source using JNDI in JDBC 2.0:

// import the JDBC packages

import java.sql.*;

import javax.sql.*;

import oracle.jdbc.pool.*;

...

InitialContext ictx = new InitialContext();

DataSource ds = (DataSource)ictx.lookup("jdbc/OracleDS");

Connection conn = ds.getConnection();

Statement stmt = conn.createStatement();

ResultSet rs = stmt.executeQuery("SELECT last_name FROM employees");

Overview of Java Support Built Into the Database

1-10 Oracle Database Application Developer’s Guide - Fundamentals

while ( rs.next() ) {

out.println( rs.getString("ename") + "<br>");

}

conn.close();

Sample Pre-2.0 JDBC Program

The following source code registers an Oracle JDBC thin driver, connects to the

database, creates a Statement object, executes a query, and processes the result set.

The SELECT statement retrieves and lists the contents of the last_name column of

the hr.employees table.

import java.sql.*

import java.math.*

import java.io.*

import java.awt.*

class JdbcTest {

public static void main (String args []) throws SQLException {

// Load Oracle driver

DriverManager.registerDriver (new oracle.jdbc.OracleDriver());

// Connect to the local database

Connection conn =

DriverManager.getConnection ("jdbc:oracle:thin:@myhost:1521:orcl",

"hr", "hr");

// Query the employee names

Statement stmt = conn.createStatement ();

ResultSet rset = stmt.executeQuery ("SELECT last_name FROM employees");

// Print the name out

while (rset.next ())

System.out.println (rset.getString (1));

// Close the result set, statement, and the connection

rset.close();

stmt.close();

conn.close();

}

One Oracle Database extension to the JDBC drivers is a form of the

getConnection() method that uses a Properties object. The Properties object

lets you specify user, password, and database information as well as row prefetching

and execution batching.

To use the OCI driver in this code, replace the Connection statement with the

following, where MyHostString is an entry in the tnsnames.ora file:

Connection conn = DriverManager.getConnection ("jdbc:oracle:oci8:@MyHostString",

"hr", "hr");

If you are creating an applet, then the getConnection() and registerDriver()

strings will be different.

JDBC in SQLJ Applications

JDBC code and SQLJ code (see "Overview of Oracle SQLJ" on page 1-11) interoperate,

allowing dynamic SQL statements in JDBC to be used with both static and dynamic

SQL statements in SQLJ. A SQLJ iterator class corresponds to the JDBC result set.

Overview of Java Support Built Into the Database

Orientation to Oracle Programmatic Environments 1-11

Overview of Oracle SQLJ

SQLJ is an ANSI SQL-1999 standard for embedding SQL statements in Java source

code. SQLJ provides a simpler alternative to JDBC for both client-side and server-side

SQL data access from Java.

A SQLJ source file contains Java source with embedded SQL statements. Oracle SQLJ

supports dynamic as well as static SQL. Support for dynamic SQL is an Oracle

extension to the SQLJ standard.

Oracle Database provides a translator and a run time driver to support SQLJ. The SQLJ

translator is 100% pure Java and is portable to any JVM that is compliant with JDK

version 1.1 or higher.

The Oracle SQLJ translator performs the following tasks:

■Translates SQLJ source to Java code with calls to the SQLJ run time driver. The

SQLJ translator converts the source code to pure Java source code and can check

the syntax and semantics of static SQL statements against a database schema and

verify the type compatibility of host variables with SQL types.

■Compiles the generated Java code with the Java compiler.

■(Optional) Creates profiles for the target database. SQLJ generates "profile" files

with customization specific to Oracle Database.

Oracle Database supports SQLJ stored procedures, functions, and triggers which

execute in the Oracle JVM. SQLJ is integrated with JDeveloper. Source-level debugging

support for SQLJ is available in JDeveloper.

The following is an example of a simple SQLJ executable statement, which returns one

value because employee_id is unique in the employee table:

String name;

#sql { SELECT first_name INTO :name FROM employees WHERE employee_id=112 };

System.out.println("Name is " + name + ", employee number = " + employee_id);

Each host variable (or qualified name or complex Java host expression) included in a

SQL expression is preceded by a colon (:). Other SQLJ statements declare Java types.

For example, you can declare an iterator (a construct related to a database cursor) for

queries that retrieve many values, as follows:

#sql iterator EmpIter (String EmpNam, int EmpNumb);

See Also: Oracle Database JDBC Developer's Guide and Reference for

more information on JDBC

Note: The term "SQLJ," when used in this manual, refers to the

Oracle SQLJ implementation, including Oracle SQLJ extensions.

See Also: For more examples and details on Oracle SQLJ syntax:

■Oracle Database JPublisher User's Guide

■Sample SQLJ code available on the Oracle Technology Network

Web site: http://www.oracle.com/technology/

Overview of Java Support Built Into the Database

1-12 Oracle Database Application Developer’s Guide - Fundamentals

Benefits of SQLJ

Oracle SQLJ extensions to Java allow rapid development and easy maintenance of

applications that perform database operations through embedded SQL.

In particular, Oracle SQLJ does the following:

■Provides a concise, legible mechanism for database access from static SQL. Most

SQL in applications is static. SQLJ provides more concise and less error-prone

static SQL constructs than JDBC does.

■Provides an SQL Checker module for verification of syntax and semantics at

translate time.

■Provides flexible deployment configurations, which makes it possible to

implement SQLJ on the client, server, or middle tier.

■Supports a software standard. SQLJ is an effort of a group of vendors and will be

supported by all of them. Applications can access multiple database vendors.

■Provides source code portability. Executables can be used with all of the vendor

DBMSs if the code does not rely on any vendor-specific features.

■Enforces a uniform programming style for the clients and the servers.

■Integrates the SQLJ translator with Oracle JDeveloper, a graphical IDE that

provides SQLJ translation, Java compilation, profile customizing, and debugging

at the source code level, all in one step.

■Includes Oracle type extensions. Datatypes supported include: LOB datatypes,

ROWID, REF CURSOR, VARRAY, nested table, user-defined object types, RAW, and

NUMBER.

Comparing SQLJ with JDBC

JDBC provides a complete dynamic SQL interface from Java to databases. It gives

developers full control over database operations. SQLJ simplifies Java database

programming to improve development productivity.

JDBC provides fine-grained control of the execution of dynamic SQL from Java,

whereas SQLJ provides a higher-level binding to SQL operations in a specific database

schema. Following are some differences between JDBC and SQLJ:

■SQLJ source code is more concise than equivalent JDBC source code.

■SQLJ uses database connections to type-check static SQL code. JDBC, being a

completely dynamic API, does not.

■SQLJ provides strong typing of query outputs and return parameters and allows

type-checking on calls. JDBC passes values to and from SQL without compile-time

type checking.

■SQLJ programs allow direct embedding of Java bind expressions within SQL

statements. JDBC requires a separate get or set statement for each bind variable

and specifies the binding by position number.

■SQLJ provides simplified rules for calling SQL stored procedures and functions.

For example, the following JDBC excerpt requires a generic call to a stored

procedure or function, in this case fun, to have the following syntax. (This

example shows SQL92 and Oracle JDBC syntaxes. Both are allowed.)

prepStmt.prepareCall("{call fun(?,?)}"); //stored procedure SQL92

prepStmt.prepareCall("{? = call fun(?,?)}"); //stored function SQL92

prepStmt.prepareCall("begin fun(:1,:2);end;"); //stored procedure Oracle

prepStmt.prepareCall("begin :1 := fun(:2,:3);end;");//stored func Oracle

Overview of Java Support Built Into the Database

Orientation to Oracle Programmatic Environments 1-13

Following is the SQLJ equivalent:

#sql {call fun(param_list) }; //Stored procedure

// Declare x

...

#sql x = {VALUES(fun(param_list)) }; // Stored function

// where VALUES is the SQL construct

The following benefits are common to SQLJ and JDBC:

■SQLJ source files can contain JDBC calls. SQLJ and JDBC are interoperable.

■Oracle JPublisher generates custom Java classes to be used in your SQLJ or JDBC

application for mappings to Oracle object types and collections.

■Java and PL/SQL stored procedures can be used interchangeably.

SQLJ Stored Procedures in the Server

SQLJ applications can be stored and executed in the server by using the following

techniques:

■Translate, compile, and customize the SQLJ source code on a client and load the

generated classes and resources into the server with the loadjava utility. The

classes are typically stored in a Java archive (.jar) file.

■Load the SQLJ source code into the server, also using loadjava, where it is

translated and compiled by the server's embedded translator.

Overview of Oracle JPublisher

Oracle JPublisher is a code generator that automates the process of creating

database-centric Java classes by hand. Oracle JPublisher is a client-side utility and is

built into the database system. You can run Oracle JPublisher from the command line

or directly from the Oracle JDeveloper IDE.

Oracle JPublisher inspects PL/SQL packages and database object types such as SQL

object types, VARRAY types, and nested table types, and then generates a Java class

that is a wrapper around the PL/SQL package with corresponding fields and

methods.

The generated Java class can be incorporated and used by Java clients or J2EE

components to exchange and transfer object type instances to and from the database

transparently.

Overview of Java Stored Procedures

Java stored procedures enable you to implement programs that run in the database

server and which are independent of programs that run in the middle tier. Structuring

applications in this way reduces complexity and increases reuse, security,

performance, and scalability.

For example, you can create a Java stored procedure that performs operations that

require data persistence and a separate program to perform presentation or business

logic operations.

See Also: Oracle Database JPublisher User's Guide for more

information on using stored procedures with Oracle SQLJ

See Also: Oracle Database JPublisher User's Guide

Overview of Java Support Built Into the Database

1-14 Oracle Database Application Developer’s Guide - Fundamentals

Java stored procedures interface with SQL by using a similar execution model as

PL/SQL.

Overview of Oracle Database Web Services

Web services represent a distributed computing paradigm for Java application

development that is an alternative to earlier Java protocols such as JDBC. It allows

application-to-application interaction by means of the XML and Web protocols. For

example, an electronics parts vendor can provide a Web-based programmatic interface

to its suppliers for inventory management. The vendor can call a Web service as part

of a program and automatically order new stock based on the data returned.

The key technologies used in Web services are:

■Web Services Description Language (WSDL), which is a standard format for

creating an XML document. WSDL describes what a web service can do, where it

resides, and how to invoke it. Specifically, it describes the operations and

parameters, including parameter types, provided by a Web service. In addition, a

WSDL document describes the location, the transport protocol, and the invocation

style for the Web service.

■Simple Object Access Protocol (SOAP) messaging, which is an XML-based

message protocol used by Web services. SOAP does not prescribe a specific

transport mechanism such as HTTP, FTP, SMTP, or JMS; however, most Web

services accept messages that use HTTP or HTTPS.

■Universal Description, Discovery, and Integration (UDDI) business registry, which

is a directory that lists Web services on the internet. The UDDI registry is often

compared to a telephone directory, listing unique identifiers (white pages),

business categories (yellow pages), and instructions for binding to a service

protocol (green pages).

Web services can use a variety of techniques and protocols. For example:

■Dispatching can occur in a synchronous (typical) or asynchronous manner.

■You can perform invocation in an RPC-style operation in which arguments are

sent and a response returned, or in a message style such as a one-way SOAP

document exchange.

■You can use different encoding rules: literal or encoded.

You can invoke a Web service statically, in which case you may know everything about

it beforehand, or dynamically, in which case you can discover its operations and

transport endpoints on the fly.

Oracle Database as a Web Service Provider

Oracle Database can function as either a Web service provider or as a Web service

consumer. When used as a provider, the database enables sharing and disconnected

access to stored procedures, data, metadata, and other database resources such as the

queuing and messaging systems.

As a Web service provider, Oracle Database provides a disconnected and

heterogeneous environment that:

■Exposes stored procedures independently of the language in which the procedures

are written

■Exposes SQL Queries and XQuery

See Also: Oracle Database Java Developer's Guide

Overview of Pro*C/C++

Orientation to Oracle Programmatic Environments 1-15

Overview of Writing Procedures and Functions in Java

Functions and procedures are named blocks that encapsulate a sequence of statements.

They are like building blocks that you can use to construct modular, maintainable

applications. You write these named blocks and then define them by using the

loadjava command or SQL CREATE FUNCTION, CREATE PROCEDURE, or CREATE

PACKAGE statements. These Java methods can accept arguments and are callable from:

■SQL CALL statements

■Embedded SQL CALL statements

■PL/SQL blocks, subprograms, and packages

■DML statements (INSERT, UPDATE, DELETE, and SELECT)

■Oracle development tools such as OCI, Pro*C/C++, and Oracle Developer

■Oracle Java interfaces such as JDBC, SQLJ statements, CORBA, and Enterprise

Java Beans

■Method calls from object types

Overview of Writing Database Triggers in Java

A database trigger is a stored procedure that Oracle Database invokes ("fires")

automatically when certain events occur, for example, when a DML operation

modifies a certain table. Triggers enforce business rules, prevent incorrect values from

being stored, and reduce the need to perform checking and cleanup operations in each

application.

Why Use Java for Stored Procedures and Triggers?

■Stored procedures and triggers are compiled once, are easy to use and maintain,

and require less memory and computing overhead.

■Network bottlenecks are avoided, and response time is improved. Distributed

applications are easier to build and use.

■Computation-bound procedures run faster in the server.

■Data access can be controlled by letting users have only stored procedures and

triggers that execute with their definer's privileges instead of invoker's rights.

■PL/SQL and Java stored procedures can call each other.

■Java in the server follows the Java language specification and can use the SQLJ

standard, so that databases other than Oracle Database are also supported.

■Stored procedures and triggers can be reused in different applications as well as

different geographic sites.

Overview of Pro*C/C++

The Pro*C/C++ precompiler is a software tool that allows the programmer to embed

SQL statements in a C or C++ source file. Pro*C/C++ reads the source file as input and

outputs a C or C++ source file that replaces the embedded SQL statements with Oracle

runtime library calls and is then compiled by the C or C++ compiler.

When there are errors found during the precompilation or the subsequent compilation,

modify your precompiler input file and re-run the two steps.

Overview of Pro*C/C++

1-16 Oracle Database Application Developer’s Guide - Fundamentals

Implementing a Pro*C/C++ Application

The following is a simple code fragment from a C source file that queries the table

employees in the schema hr:

...

#define UNAME_LEN 10

...

int emp_number;

/* Define a host structure for the output values of a SELECT statement. */

/* No declare section needed if precompiler option MODE=ORACLE */

struct {

VARCHAR last_name[UNAME_LEN];

float salary;

float commission_pct;

} emprec;

/* Define an indicator structure to correspond to the host output structure. */

struct {

short emp_name_ind;

short sal_ind;

short comm_ind;

} emprec_ind;

...

/* Select columns last_name, salary, and commission_pct given the user's input

/* for employee_id. */

EXEC SQL SELECT last_name, salary, commission_pct

INTO :emprec INDICATOR :emprec_ind

FROM employees

WHERE employee_id = :emp_number;

...

The embedded SELECT statement is only slightly different from an interactive

(SQL*Plus) SELECT statement. Every embedded SQL statement begins with EXEC

SQL. The colon (:), precedes every host (C) variable. The returned values of data and

indicators (set when the data value is NULL or character columns have been truncated)

can be stored in structs (such as in the preceding code fragment), in arrays, or in arrays

of structs. Multiple result set values are handled very simply in a manner that

resembles the case shown, where there is only one result, because of the unique

employee number. You use the actual names of columns and tables in embedded SQL.

Use the default precompiler option values, or you can enter values which give you

control over the use of resources, how errors are reported, the formatting of output,

and how cursors (which correspond to a particular connection or SQL statement) are

managed. Cursors are used when there are multiple result set values.

Enter the options either in a configuration file, on the command line, or in-line inside

your source code with a special statement that begins with EXEC ORACLE. If there are

no errors found, you can then compile, link, and execute the output source file, like

any other C program that you write.

Use the precompiler to create server database access from clients that can be on many

different platforms. Pro*C/C++ allows you the freedom to design your own user

interfaces and to add database access to existing applications.

Before writing your embedded SQL statements, you may want to test interactive

versions of the SQL in SQL*Plus. You then make only minor changes to start testing

your embedded SQL application.

Overview of Pro*C/C++

Orientation to Oracle Programmatic Environments 1-17

Highlights of Pro*C/C++ Features

The following is a short subset of the capabilities of Pro*C/C++. For complete details,

refer to the Pro*C/C++ Precompiler Programmer's Guide.

■You can write your application in either C or C++.

■You can write multithreaded programs if your platform supports a threads

package. Concurrent connections are supported in either single-threaded or

multithreaded applications.

■You can improve performance by embedding PL/SQL blocks. These blocks can

call functions or procedures in Java or PL/SQL that are written by you or

provided in Oracle Database packages.

■Using precompiler options, you can check the syntax and semantics of your SQL

or PL/SQL statements during precompilation, as well as at runtime.

■You can call stored PL/SQL and Java subprograms. Modules written in COBOL or

in C can be called from Pro*C/C++. External C procedures in shared libraries are

callable by your program.

■You can conditionally precompile sections of your code so that they can execute in

different environments.

■You can use arrays, or structures, or arrays of structures as host and indicator

variables in your code to improve performance.

■You can deal with errors and warnings so that data integrity is guaranteed. As a

programmer, you control how errors are handled.

■Your program can convert between internal datatypes and C language datatypes.

■The Oracle Call Interface (OCI) and Oracle C++ Call Interface (OCCI), lower-level

C and C++ interfaces, are available for use in your precompiler source.

■Pro*C/C++ supports dynamic SQL, a technique that allows users to input variable

values and statement syntax.

■Pro*C/C++ can use special SQL statements to manipulate tables containing

user-defined object types. An Object Type Translator (OTT) will map the object

types and named collection types in your database to structures and headers that

you will then include in your source.

■Two kinds of collection types, nested tables and VARRAY, are supported with a set

of SQL statements that allow a high degree of control over data.

■Large Objects are accessed by another set of SQL statements.

■A new ANSI SQL standard for dynamic SQL is supported for new applications, so

that you can execute SQL statements with a varying number of host variables. An

older technique for dynamic SQL is still usable by pre-existing applications.

■Globalization support lets you use multibyte characters and UCS2 Unicode data.

■Using scrollable cursors, you can move backward and forward through a result

set. For example, you can fetch the last row of the result set, or jump forward or

backward to an absolute or relative position within the result set.

■A connection pool is a group of physical connections to a database that can be

shared by several named connections. Enabling the connection pool option can

help to optimize the performance of Pro*C/C++ application. The connection pool

option is not enabled by default.

Overview of Pro*COBOL

1-18 Oracle Database Application Developer’s Guide - Fundamentals

Overview of Pro*COBOL

The Pro*COBOL precompiler is a software tool that allows the programmer to embed

SQL statements in a COBOL source code file. Pro*COBOL reads the source file as

input and outputs a COBOL source file that replaces the embedded SQL statements

with Oracle Database runtime library calls, and is then compiled by the COBOL

compiler.

When there are errors found during the precompilation or the subsequent compilation,

modify your precompiler input file and re-run the two steps.

How You Implement a Pro*COBOL Application

Here is a simple code fragment from a source file that queries the table employees in

the schema hr:

...

WORKING-STORAGE SECTION.

* DEFINE HOST INPUT AND OUTPUT HOST AND INDICATOR VARIABLES.

* NO DECLARE SECTION NEEDED IF MODE=ORACLE.

01 EMP-REC-VARS.

05 EMP-NAME PIC X(10) VARYING.

05 EMP-NUMBER PIC S9(4) COMP VALUE ZERO.

05 SALARY PIC S9(5)V99 COMP-3 VALUE ZERO.

05 COMMISSION PIC S9(5)V99 COMP-3 VALUE ZERO.

05 COMM-IND PIC S9(4) COMP VALUE ZERO.

...

PROCEDURE DIVISION.

...

EXEC SQL

SELECT last_name, salary, commission_pct

INTO :EMP-NAME, :SALARY, :COMMISSION:COMM-IND

FROM employees

WHERE employee_id = :EMP-NUMBER

END-EXEC.

...

The embedded SELECT statement is only slightly different from an interactive

(SQL*Plus) SELECT statement. Every embedded SQL statement begins with EXEC

SQL. The colon (:) precedes every host (COBOL) variable. The SQL statement is

terminated by END-EXEC. The returned values of data and indicators (set when the

data value is NULL or character columns have been truncated) can be stored in group

items (such as in the preceding code fragment), in tables, or in tables of group items.

Multiple result set values are handled very simply in a manner that resembles the case

shown, where there is only one result, given the unique employee number. You use the

actual names of columns and tables in embedded SQL.

Use the default precompiler option values, or enter values that give you control over

the use of resources, how errors are reported, the formatting of output, and how

cursors are managed (cursors correspond to a particular connection or SQL statement).

Enter the options in a configuration file, on the command line, or in-line inside your

source code with a special statement that begins with EXEC ORACLE. If there are no

errors found, you can then compile, link, and execute the output source file, like any

other COBOL program that you write.

Overview of OCI and OCCI

Orientation to Oracle Programmatic Environments 1-19

Use the precompiler to create server database access from clients that can be on many

different platforms. Pro*COBOL allows you the freedom to design your own user

interfaces and to add database access to existing COBOL applications.

The embedded SQL statements available conform to an ANSI standard, so that you

can access data from many databases in a program, including remote servers

networked through Oracle Net.

Before writing your embedded SQL statements, you may want to test interactive

versions of the SQL in SQL*Plus. You then make only minor changes to start testing

your embedded SQL application.

Highlights of Pro*COBOL Features

The following is a short subset of the capabilities of Pro*COBOL.

■You can call stored PL/SQL or Java subprograms. You can improve performance

by embedding PL/SQL blocks. These blocks can call PL/SQL functions or

procedures written by you or provided in Oracle Database packages.

■Precompiler options allow you to define how cursors, errors, syntax-checking, file

formats, and so on, are handled.

■Using precompiler options, you can check the syntax and semantics of your SQL

or PL/SQL statements during precompilation, as well as at runtime.

■You can conditionally precompile sections of your code so that they can execute in

different environments.

■Use tables, or group items, or tables of group items as host and indicator variables

in your code to improve performance.

■You can program how errors and warnings are handled, so that data integrity is

guaranteed.

■Pro*COBOL supports dynamic SQL, a technique that allows users to input

variable values and statement syntax.

Overview of OCI and OCCI

The Oracle Call Interface (OCI) and Oracle C++ Call Interface (OCCI) are application

programming interfaces (APIs) that allow you to create applications that use native

procedures or function calls of a third-generation language to access Oracle Database

and control all phases of SQL statement execution. These APIs provide:

■Improved performance and scalability through the efficient use of system memory

and network connectivity

■Consistent interfaces for dynamic session and transaction management in a

two-tier client/server or multitier environment

■N-tiered authentication

■Comprehensive support for application development using Oracle objects

■Access to external databases

■Ability to develop applications that service an increasing number of users and

requests without additional hardware investments

See Also: Pro*COBOL Programmer's Guide for complete details

Overview of OCI and OCCI

1-20 Oracle Database Application Developer’s Guide - Fundamentals

OCI lets you manipulate data and schemas in a database using a host programming

language, such as C. OCCI is an object-oriented interface suitable for use with C++.

These APIs provide a library of standard database access and retrieval functions in the

form of a dynamic runtime library (OCILIB) that can be linked in an application at

runtime. This eliminates the need to embed SQL or PL/SQL within 3GL programs.

Advantages of OCI

OCI provides significant advantages over other methods of accessing Oracle Database:

■More fine-grained control over all aspects of the application design.

■High degree of control over program execution.

■Use of familiar 3GL programming techniques and application development tools

such as browsers and debuggers.

■Support of dynamic SQL, method 4.

■Availability on the broadest range of platforms of all the Oracle programmatic

interfaces.

■Dynamic bind and define using callbacks.

■Describe functionality to expose layers of server metadata.

■Asynchronous event notification for registered client applications.

■Enhanced array data manipulation language (DML) capability for array INSERTs,

UPDATEs, and DELETEs.

■Ability to associate a commit request with an execute to reduce round-trips.

■Optimization for queries using transparent prefetch buffers to reduce round-trips.

■Thread safety, so you do not have to implement mutual exclusion (mutex) locks on

OCI handles.

■The server connection in nonblocking mode means that control returns to the OCI

code when a call is still executing or could not complete.

Parts of the OCI

The OCI encompasses four main sets of functionality:

■OCI relational functions, for managing database access and processing SQL

statements

■OCI navigational functions, for manipulating objects retrieved from an Oracle

Database

■OCI datatype mapping and manipulation functions, for manipulating data attributes

of Oracle types

■OCI external procedure functions, for writing C callbacks from PL/SQL

See Also: For more information about OCI and OCCI calls:

■Oracle Call Interface Programmer's Guide

■Oracle C++ Call Interface Programmer's Guide

■Oracle Streams Advanced Queuing User's Guide and Reference

■Oracle Database Globalization Support Guide

■Oracle Database Data Cartridge Developer's Guide

Overview of OCI and OCCI

Orientation to Oracle Programmatic Environments 1-21

Procedural and Non-Procedural Elements

The Oracle Call Interface (OCI) enables you to develop applications that combine the

non-procedural data access power of SQL with the procedural capabilities of most

programming languages, including C and C++. Note the following characteristics of

procedural and non-procedural languages:

■In a non-procedural language program, the set of data to be operated on is

specified, but what operations will be performed and how the operations are to be

carried out is not specified. The non-procedural nature of SQL makes it an easy

language to learn and to use to perform database transactions. It is also the

standard language used to access and manipulate data in modern relational and

object-relational database systems.

■In a procedural language program, the execution of most statements depends on

previous or subsequent statements and on control structures, such as loops or

conditional branches, which are not available in SQL. The procedural nature of

these languages makes them more complex than SQL, but it also makes them very

flexible and powerful.

The combination of both non-procedural and procedural language elements in an OCI

program provides easy access to Oracle Database in a structured programming

environment.

The OCI supports all SQL data definition, data manipulation, query, and transaction

control facilities that are available through Oracle Database. For example, an OCI

program can run a query against Oracle Database. The queries can require the

program to supply data to the database using input (bind) variables, as follows:

SELECT name FROM employees WHERE empno = :empnumber

In the preceding SQL statement,:empnumber is a placeholder for a value that will be

supplied by the application.

You can alternatively use PL/SQL, Oracle's procedural extension to SQL. The

applications you develop can be more powerful and flexible than applications written

in SQL alone. The OCI also provides facilities for accessing and manipulating objects

in Oracle Database.

Building an OCI Application

As Figure 1–1 shows, you compile and link an OCI program in the same way that you

compile and link a non-database application. There is no need for a separate

preprocessing or precompilation step.

Overview of Oracle Data Provider for .NET (ODP.NET)

1-22 Oracle Database Application Developer’s Guide - Fundamentals

Figure 1–1 The OCI Development Process

Overview of Oracle Data Provider for .NET (ODP.NET)

Oracle Data Provider for .NET (ODP.NET) is an implementation of a data provider for

Oracle Database.

ODP.NET uses APIs native to Oracle Database to offer fast and reliable access from

any .NET application to database features and data. It also uses and inherits classes

and interfaces available in the Microsoft .NET Framework Class Library.

For programmers using Oracle Provider for OLE DB, ADO (ActiveX Data Objects)

provides an automation layer that exposes an easy programming model. ADO.NET

provides a similar programming model, but without the automation layer, for better

performance. More importantly, the ADO.NET model allows native providers such as

ODP.NET to expose specific features and datatypes specific to Oracle Database.

Using ODP.NET in a Simple Application

The following is a simple C# application that connects to Oracle Database and displays

its version number before disconnecting.

using System;

using Oracle.DataAccess.Client;

class Example

{

OracleConnection con;

void Connect()

Note: To properly link your OCI programs, it may be necessary on

some platforms to include other libraries, in addition to the OCI

library. Check your Oracle platform-specific documentation for

further information about extra libraries that may be required.

See Also: Oracle Data Provider for .NET Developer's Guide

Host Language Compiler

Source Files

Host Linker

Application

Object Files OCI Library

Object

Server

Overview of Oracle Objects for OLE (OO4O)

Orientation to Oracle Programmatic Environments 1-23

{

con = new OracleConnection();

con.ConnectionString = "User Id=hr;Password=hr;Data Source=oracle";

con.Open();

Console.WriteLine("Connected to Oracle" + con.ServerVersion);

}

void Close()

{

con.Close();

con.Dispose();

}

static void Main()

{

Example example = new Example();

example.Connect();

example.Close();

}

Overview of Oracle Objects for OLE (OO4O)

Oracle Objects for OLE (OO4O) is a product designed to allow easy access to data

stored in Oracle Database with any programming or scripting language that supports

the Microsoft COM Automation and ActiveX technology. This includes Visual Basic,

Visual C++, Visual Basic For Applications (VBA), IIS Active Server Pages (VBScript

and JavaScript), and others.

See the OO4O online help for detailed information about using OO4O.

Oracle Objects for OLE consists of the following software layers:

■ OO4O "In-Process" Automation Server

■Oracle Data Control

■Oracle Objects for OLE C++ Class Library

Figure 1–2, "Software Layers" illustrates the OO4O software components.

Note: Additional samples are provided in directory ORACLE_

BASE\ORACLE_HOME\ODP.NET\Samples.

Overview of Oracle Objects for OLE (OO4O)

1-24 Oracle Database Application Developer’s Guide - Fundamentals

Figure 1–2 Software Layers

OO4O Automation Server

The OO4O Automation Server is a set of COM Automation objects for connecting to

Oracle Database, executing SQL statements and PL/SQL blocks, and accessing the

results.

Unlike other COM-based database connectivity APIs, such as Microsoft ADO, the

OO4O Automation Server has been developed and evolved specifically for use with

Oracle Database.

It provides an optimized API for accessing features that are unique to Oracle Database

and are otherwise cumbersome or inefficient to use from ODBC or OLE

database-specific components.

OO4O provides key features for accessing Oracle Database efficiently and easily in

environments ranging from the typical two-tier client/server applications, such as

those developed in Visual Basic or Excel, to application servers deployed in

multitiered application server environments such as Web server applications in

Microsoft Internet Information Server (IIS) or Microsoft Transaction Server (MTS).

Features include:

■Support for execution of PL/SQL and Java stored procedures, and PL/SQL

anonymous blocks. This includes support for Oracle datatypes used as parameters

to stored procedures, including PL/SQL cursors. Refer to "Support for Oracle LOB

and Object Datatypes" on page 1-28.

■Support for scrollable and updatable cursors for easy and efficient access to result

sets of queries.

■Thread-safe objects and Connection Pool Management Facility for developing

efficient Web server applications.

■Full support for Oracle object-relational and LOB datatypes.

Data Aware

ActiveX

Controls

Oracle Data

Control

Oracle Client

Libraries

(OCI, CORE,

NLS)

Oracle

Database

OO4O

In-Process

Automation

Server

COM/DCOM

Automation

Controllers

(VB, Excel, ASP)

C++ Class

Libraries

Overview of Oracle Objects for OLE (OO4O)

Orientation to Oracle Programmatic Environments 1-25

■Full support for Advanced Queuing.

■Support for array inserts and updates.

■Support for Microsoft Transaction Server (MTS).

OO4O Object Model

The Oracle Objects for OLE object model is illustrated in Figure 1–3, "Objects and Their

Relations".

Figure 1–3 Objects and Their Relations

OraSession

An OraSession object manages collections of OraDatabase, OraConnection, and

OraDynaset objects used within an application.

Typically, a single OraSession object is created for each application, but you can create

named OraSession objects for shared use within and between applications.

The OraSession object is the top-most object for an application. It is the only object

created by the CreateObject VB/VBA API and not by an Oracle Objects for OLE

method. The following code fragment shows how to create an OraSession object:

Dim OraSession as Object

Set OraSession = CreateObject("OracleInProcServer.XOraSession")

OraServer

OraServer represents a physical network connection to Oracle Database.

The OraServer interface is introduced to expose the connection-multiplexing feature

provided in the Oracle Call Interface. After an OraServer object is created, multiple

user sessions (OraDatabase) can be attached to it by invoking the OpenDatabase

method. This feature is particularly useful for application components, such as

Internet Information Server (IIS), that use Oracle Objects for OLE in n-tier distributed

environments.

OraParameter

OraParameters

OraParamArray

OraSession

OraDatabase

OraField

OraMDAttribute

OraSQLStmt

OraDynaset

OraMetaData

OraAQ OraAQMsg

OraServer

Overview of Oracle Objects for OLE (OO4O)

1-26 Oracle Database Application Developer’s Guide - Fundamentals

The use of connection multiplexing when accessing Oracle Database with a large

number of user sessions active can help reduce server processing and resource

requirements while improving server scalability.

OraServer is used to share a single connection across multiple OraDatabase objects

(multiplexing), whereas each OraDatabase obtained from an OraSession has its own

physical connection.

OraDatabase

An OraDatabase interface adds additional methods for controlling transactions and

creating interfaces representing of Oracle object types. Attributes of schema objects can

be retrieved using the Describe method of the OraDatabase interface.

In releases prior to Oracle8i, an OraDatabase object is created by invoking the

OpenDatabase method of an OraSession interface. The Oracle Net alias, user

name, and password are passed as arguments to this method. In Oracle8i and later,

invocation of this method results in implicit creation of an OraServer object.

An OraDatabase object can also be created using the OpenDatabase method of the

OraServer interface.

Transaction control methods are available at the OraDatabase (user session) level.

Transactions may be started as Read-Write (default), Serializable, or

Read-only. Transaction control methods include:

■BeginTrans

■CommitTrans

■RollbackTrans

For example:

UserSession.BeginTrans(OO4O_TXN_READ_WRITE)

UserSession.ExecuteSQL("delete emp where empno = 1234")

UserSession.CommitTrans

OraDynaset

An OraDynaset object permits browsing and updating of data created from a SQL

SELECT statement.

The OraDynaset object can be thought of as a cursor, although in actuality several

real cursors may be used to implement the semantics of OraDynaset. An

OraDynaset object automatically maintains a local cache of data fetched from the

server and transparently implements scrollable cursors within the browse data. Large

queries may require significant local disk space; application developers are

encouraged to refine queries to limit disk usage.

OraField

An OraField object represents a single column or data item within a row of a

dynaset.

If the current row is being updated, then the OraField object represents the currently

updated value, although the value may not yet have been committed to the database.

Assignment to the Value property of a field is permitted only if a record is being

edited (using Edit) or a new record is being added (using AddNew). Other attempts to

assign data to a field's Value property results in an error.

Overview of Oracle Objects for OLE (OO4O)

Orientation to Oracle Programmatic Environments 1-27

OraMetaData and OraMDAttribute

An OraMetaData object is a collection of OraMDAttribute objects that represent the

description information about a particular schema object in the database.

The OraMetaData object can be visualized as a table with three columns:

■Metadata Attribute Name

■Metadata Attribute Value

■Flag specifying whether the Value is another OraMetaData object

The OraMDAttribute objects contained in the OraMetaData object can be accessed

by subscripting using ordinal integers or by using the name of the property.

Referencing a subscript that is not in the collection results in the return of a NULL

OraMDAttribute object.

OraParameters and OraParameter

An OraParameter object represents a bind variable in a SQL statement or PL/SQL

block.

OraParameter objects are created, accessed, and removed indirectly through the

OraParameters collection of an OraDatabase object. Each parameter has an

identifying name and an associated value. You can automatically bind a parameter to

SQL and PL/SQL statements of other objects (as noted in the object descriptions), by

using the parameter name as a placeholder in the SQL or PL/SQL statement. Such use

of parameters can simplify dynamic queries and increase program performance.

OraParamArray

An OraParamArray object represents an array-type bind variable in a SQL statement

or PL/SQL block, as opposed to a scalar-type bind variable represented by the

OraParameter object.

OraParamArray objects are created, accessed, and removed indirectly through the

OraParameters collection of an OraDatabase object. Each OraParamArray object

has an identifying name and an associated value.

OraSQLStmt

An OraSQLStmt object represents a single SQL statement. Use the CreateSQL

method to create an OraSQLStmt object from an OraDatabase object.

During create and refresh, OraSQLStmt objects automatically bind all relevant,

enabled input parameters to the specified SQL statement, using the parameter names

as placeholders in the SQL statement. This can improve the performance of SQL

statement execution without re-parsing the SQL statement.

The OraSQLStmt object can be used later to execute the same query using a different

value for the :SALARY placeholder. This is done as follows (updateStmt is the

OraSQLStmt object here):

OraDatabase.Parameters("SALARY").value = 200000

updateStmt.Parameters("ENAME").value = "KING"

updateStmt.Refresh

OraAQ

An OraAQ object is instantiated by invoking the CreateAQ method of the

OraDatabase interface. It represents a queue that is present in the database.

Overview of Oracle Objects for OLE (OO4O)

1-28 Oracle Database Application Developer’s Guide - Fundamentals

Oracle Objects for OLE provides interfaces for accessing Oracle Advanced Queuing

(AQ) feature. It makes AQ accessible from popular COM-based development

environments such as Visual Basic. For a detailed description of Oracle Advanced

Queuing, refer to Oracle Streams Advanced Queuing User's Guide and Reference.

OraAQMsg

The OraAQMsg object encapsulates the message to be enqueued or dequeued. The

message can be of any user-defined or raw type.

For a detailed description of Oracle Advanced Queuing, refer to Oracle Streams

Advanced Queuing User's Guide and Reference.

OraAQAgent

The OraAQAgent object represents a message recipient and is only valid for queues

that allow multiple consumers. It is a child of OraAQMsg.

An OraAQAgent object can be instantiated by invoking the AQAgent method. For

example:

Set agent = qMsg.AQAgent(name)

An OraAQAgent object can also be instantiated by invoking the AddRecipient

method. For example:

Set agent = qMsg.AddRecipient(name, address, protocol).

Support for Oracle LOB and Object Datatypes

Oracle Objects for OLE provides full support for accessing and manipulating instances

of object datatypes and LOBs in Oracle Database. Figure 1–4, "Supported Oracle

Datatypes" illustrates the datatypes supported by OO4O.

Instances of these types can be fetched from the database or passed as input or output

variables to SQL statements and PL/SQL blocks, including stored procedures and

functions. All instances are mapped to COM Automation Interfaces that provide

methods for dynamic attribute access and manipulation.

Figure 1–4 Supported Oracle Datatypes

OraAttribute

Element Values

OraObject

OraRef

OraCollection

OraField

OraParameter

OraBLOB

OraCLOB

OraBFILE

Value of all other scalar types

OraParamArray

Overview of Oracle Objects for OLE (OO4O)

Orientation to Oracle Programmatic Environments 1-29

OraBLOB and OraCLOB

The OraBlob and OraClob interfaces in Oracle Objects for OLE provide methods for

performing operations on large database objects of datatype BLOB, CLOB, and NCLOB.

BLOB, CLOB, and NCLOB datatypes are also referred to here as LOB datatypes.

LOB data is accessed using Read and the CopyToFile methods.

LOB data is modified using Write, Append, Erase, Trim, Copy, CopyFromFile,

and CopyFromBFile methods. Before modifying the content of a LOB column in a

row, a row lock must be obtained. If the LOB column is a field of an OraDynaset,

object, then the lock is obtained by invoking the Edit method.

OraBFILE

The OraBFile interface in Oracle Objects for OLE provides methods for performing

operations on large database objects of datatype BFILE.

BFILE objects are large binary data objects stored in operating system files outside of

the database tablespaces.

Oracle Data Control

Oracle Data Control (ODC) is an ActiveX Control that is designed to simplify the

exchange of data between Oracle Database and visual controls such edit, text, list, and

grid controls in Visual Basic and other development tools that support custom

controls.

ODC acts as an agent to handle the flow of information from Oracle Database and a

visual data-aware control, such as a grid control, that is bound to it. The data control

manages various user interface (UI) tasks such as displaying and editing data. It also

executes and manages the results of database queries.

Oracle Data Control is compatible with the Microsoft data control included with

Visual Basic. If you are familiar with the Visual Basic data control, learning to use

Oracle Data Control is quick and easy. Communication between data-aware controls

and a Data Control is governed by a protocol that has been specified by Microsoft.

Oracle Objects for OLE C++ Class Library

Oracle Objects for OLE C++ Class Library is a collection of C++ classes that provide

programmatic access to the Oracle Object Server. Although the class library is

implemented using OLE Automation, neither the OLE development kit nor any OLE

development knowledge is necessary to use it. This library helps C++ developers

avoid the chore of writing COM client code for accessing the OO4O interfaces.

Additional Sources of Information

For detailed information about Oracle Objects for OLE refer to the online help

provided with the OO4O product:

■ Oracle Objects for OLE Help

■ Oracle Objects for OLE C++ Class Library Help

To view examples of how to use Oracle Objects for OLE, refer to the samples located in

the ORACLE_HOME\OO4O directory of the Oracle Database installation. Additional

OO4O examples can be found in the following Oracle publications:

■ Oracle Database Application Developer's Guide - Large Objects

Choosing a Programming Environment

1-30 Oracle Database Application Developer’s Guide - Fundamentals

■ Oracle Streams Advanced Queuing User's Guide and Reference

■Oracle Database PL/SQL Packages and Types Reference

Choosing a Programming Environment

To choose a programming environment for a new development project:

■Review the preceding overviews and the manuals for each environment.

■Read the platform-specific manual that explains which compilers are approved for

use with your platforms.

■If a particular language does not provide a feature you need, remember that

PL/SQL and Java stored procedures can both be called from code written in any of

the languages in this chapter. Stored procedures include triggers and object type

methods.

■External procedures written in C can be called from OCI, Java, PL/SQL or SQL.

The external procedure itself can call back into the database using either SQL, OCI,

or Pro*C (but not C++).

The following examples illustrate easy choices:

■Pro*COBOL does not support object types or collection types, while Pro*C/C++

does.

■SQLJ does not support dynamic SQL the way that JDBC does.

Choosing Whether to Use OCI or a Precompiler

Precompiler applications typically contain less code than equivalent OCI applications,

which can help productivity.

Some situations require detailed control of the database and are suited for OCI

applications (either pure OCI or a precompiler application with embedded OCI calls):

■OCI provides more detailed control over multiplexing and migrating sessions.

■OCI provides dynamic bind and define using callbacks that can be used for any

arbitrary structure, including lists.

■OCI has many calls to handle metadata.

■OCI allows asynchronous event notifications to be received by a client application.

It provides a means for clients to generate notifications for propagation to other

clients.

■OCI allows DML statements to use arrays to complete as many iterations as

possible before returning any error messages.

■OCI calls for special purposes include Advanced Queuing, globalization support,

Data Cartridges, and support of the date and time datatypes.

■OCI calls can be embedded in a Pro*C/C++ application.

Using Built-In Packages and Libraries

Both Java and PL/SQL have built-in packages and libraries.

PL/SQL and Java interoperate in the server. You can execute a PL/SQL package from

Java or wrap a PL/SQL class with a Java wrapper so that it can be called from

Choosing a Programming Environment

Orientation to Oracle Programmatic Environments 1-31

distributed CORBA and EJB clients. The following table shows PL/SQL packages and

their Java equivalents:

Java Compared to PL/SQL

Both Java and PL/SQL can be used to build applications in the database. Here are

some guidelines for their use:

PL/SQL Is Optimized for Database Access

PL/SQL uses the same datatypes as SQL. SQL datatypes are thus easier to use and

SQL operations are faster than with Java, especially when a large amount of data is

involved, when mostly database access is done, or when bulk operations are used.

PL/SQL Is Integrated with the Database

PL/SQL is an extension to SQL offering data encapsulation, information hiding,

overloading, and exception-handling.

Some advanced PL/SQL capabilities are not available for Java in Oracle9i. Examples

are autonomous transactions and the dblink facility for remote databases. Code

development is usually faster in PL/SQL than in Java.

Both Java and PL/SQL Have Object-Oriented Features

Java has inheritance, polymorphism, and component models for developing

distributed systems. PL/SQL has inheritance and type evolution, the ability to change

methods and attributes of a type while preserving subtypes and table data that use the

type.

Table 1–1 PL/SQL and Java Equivalent Software

PL/SQL Package Java Equivalent

DBMS_ALERT Call package with SQLJ or JDBC.

DBMS_DDL JDBC has this functionality.

DBMS_JOB Schedule a job that has a Java Stored procedure.

DBMS_LOCK Call with SQLJ or JDBC.

DBMS_MAIL Use JavaMail.

DBMS_OUTPUT Use subclass

oracle.aurora.rdbms.OracleDBMSOutputStream or Java

stored procedure DBMS_JAVA.SET_STREAMS.

DBMS_PIPE Call with SQLJ or JDBC.

DBMS_SESSION Use JDBC to execute an ALTER SESSION statement.

DBMS_SNAPSHOT Call with SQLJ or JDBC.

DBMS_SQL Use JDBC.

DBMS_TRANSACTION Use JDBC to execute an ALTER SESSION statement.

DBMS_UTILITY Call with SQLJ or JDBC.

UTL_FILE Grant the JAVAUSERPRIV privilege and then use Java I/O entry

points.

Choosing a Programming Environment

1-32 Oracle Database Application Developer’s Guide - Fundamentals

Java Is Used for Open Distributed Applications

Java has a richer type system than PL/SQL and is an object-oriented language. Java

can use CORBA (which can have many different computer languages in its clients) and

EJB. PL/SQL packages can be called from CORBA or EJB clients.

You can run XML tools, the Internet File System, or JavaMail from Java.

Many Java-based development tools are available throughout the industry.

Part I

SQL for Application Developers

This part contains the following chapters:

■Chapter 2, "SQL Processing for Application Developers"

■Chapter 3, "Using SQL Datatypes in Application Development"

■Chapter 4, "Using Regular Expressions in Oracle Database"

■Chapter 5, "Using Indexes in Application Development"

■Chapter 6, "Maintaining Data Integrity in Application Development"

SQL Processing for Application Developers 2-1

SQL Processing for Application Developers

This chapter describes how Oracle Database processes SQL statements. Before reading

this chapter you should read the section "SQL Processing" in Oracle Database Concepts.

Topics include the following:

■Grouping Operations into Transactions

■Ensuring Repeatable Reads with Read-Only Transactions

■Using Cursors within Applications

■Locking Data Explicitly

■About User Locks

■Using Serializable Transactions for Concurrency Control

■Autonomous Transactions

■Resuming Execution After a Storage Error Condition

Grouping Operations into Transactions

This section contains the following topics:

■Deciding How to Group Operations in Transactions

■Improving Transaction Performance

■Committing Transactions

■Rolling Back Transactions

■Defining Transaction Savepoints

Deciding How to Group Operations in Transactions

In general, only application designers who use the programming interfaces to Oracle

Database are concerned with which types of actions should be grouped together as

one transaction. You should use the following principles when deciding how to group

transactions:

■Transactions must be defined properly so that work is accomplished in logical

units and data is kept consistent.

■Data in all referenced tables should be in a consistent state before the transaction

begins and after it ends.

■Transactions should consist of only the SQL statements or PL/SQL blocks that

comprise one consistent change to the data.

Grouping Operations into Transactions

2-2 Oracle Database Application Developer’s Guide - Fundamentals

For example, suppose that you write a Web application that enables users to transfer

funds between accounts. The transaction should include the debit to one account,

which is executed by one SQL statement, and the credit to another account, which is

executed by a second SQL statement. Both statements should fail or succeed together

as a unit of work; the credit should not be committed without the debit. Other

non-related actions, such as a new deposit to one account, should not be included in

the same transaction.

Improving Transaction Performance

As an application developer, you should consider whether you can improve

performance. Consider the following performance enhancements when designing and

writing your application:

■Use the SET TRANSACTION command with the USE ROLLBACK SEGMENT clause to

explicitly assign a transaction to a rollback segment. This technique can eliminate

the need to allocate additional extents dynamically, which can reduce system

performance. Note that this clause is relevant and valid only if you use rollback

segments for undo. If you use automatic undo management, then Oracle Database

ignores this clause.

■Establish standards for writing SQL statements so that you can take advantage of

shared SQL areas. Oracle Database recognizes identical SQL statements and allows

them to share memory areas. This reduces memory usage on the database server

and increases system throughput.

■Use the ANALYZE command to collect statistics that can be used by Oracle

Database to implement a cost-based approach to SQL statement optimization. You

can supply additional "hints" to the optimizer as needed.

■Call the DBMS_APPLICATION_INFO.SET_ACTION procedure before beginning a

transaction to register and name a transaction for later use when measuring

performance across an application. You should specify which type of activity a

transaction performs so that the system tuners can later see which transactions are

taking up the most system resources.

■Increase user productivity and query efficiency by including user-written PL/SQL

functions in SQL expressions as described in "Calling Stored Functions from SQL

Expressions" on page 7-36.

■Create explicit cursors when writing a PL/SQL application.

■Reduce frequency of parsing and improve performance in precompiler programs

by increasing the number of cursors with MAX_OPEN_CURSORS.

■Use the SET TRANSACTION command with the ISOLATION LEVEL set to

SERIALIZABLE to get ANSI/ISO serializable transactions.

Committing Transactions

To commit a transaction, use the COMMIT statement. The following two statements are

equivalent and commit the current transaction:

See Also:

■"How Serializable Transactions Interact" on page 2-15

■"Using Cursors within Applications" on page 2-6

■Oracle Database Concepts for more information about transaction

tuning features

Grouping Operations into Transactions

SQL Processing for Application Developers 2-3

COMMIT WORK;

COMMIT;

The COMMIT statements lets you include the COMMENT parameter along with a

comment that provides information about the transaction being committed. This

option is useful for including information about the origin of the transaction when you

commit distributed transactions:

COMMIT COMMENT 'Dallas/Accts_pay/Trans_type 10B';

Managing Commit Redo Behavior

When a transaction updates the database, it generates a redo entry corresponding to

this update. Oracle Database buffers this redo in memory until the completion of the

transaction. When the transaction commits, the log writer (LGWR) process writes redo

for the commit, along with the accumulated redo of all changes in the transaction, to

disk. By default Oracle Database writes the redo to disk before the call returns to the

client. This behavior introduces a latency in the commit because the application must

wait for the redo to be persisted on disk.

Suppose that you are writing an application that requires very high transaction

throughput. If you are willing to trade commit durability for lower commit latency,

then you can change the default COMMIT options so that the application does not need

to wait for Oracle Database to write data to the online redo logs.

Oracle Database enables you to change the handling of commit redo depending on the

needs of your application. You can change the commit behavior in the following

locations:

■COMMIT_WRITE initialization parameter at the system or session level

■COMMIT statement

The options in the COMMIT statement override the current settings in the initialization

parameter. Table 2–1 describes redo persistence options that you can set in either

location.

The following example shows how to set the commit behavior to BATCH and NOWAIT

in the initialization parameter file:

COMMIT_WRITE = BATCH, NOWAIT

You can change the commit behavior at the system level by executing ALTER SYSTEM

as in the following example:

ALTER SYSTEM SET COMMIT_WRITE = BATCH, NOWAIT

Table 2–1 Initialization Parameter and COMMIT Options for Managing Commit Redo

Option Specifies that . . .

WAIT The commit does not return as successful until the redo corresponding to the

commit is persisted in the online redo logs (default).

NOWAIT The commit should return to the application without waiting for the redo to

be written to the online redo logs.

IMMEDIATE The log writer process should write the redo for the commit immediately

(default). In other words, this option forces a disk I/O.

BATCH Oracle Database should buffer the redo. The log writer process is permitted to

write the redo to disk in its own time.

Grouping Operations into Transactions

2-4 Oracle Database Application Developer’s Guide - Fundamentals

After the initialization parameter is set, a COMMIT statement with no options conforms

to the options specified in the parameter. Alternatively, you can override the current

initialization parameter setting by specifying options directly on the COMMIT

statement as in the following example:

COMMIT WRITE BATCH NOWAIT

In either case, your application specifies that log writer does not have to write the redo

for the commit immediately to the online redo logs and should not wait for

confirmation that the redo has been written to disk.

If your application uses OCI, then you can modify redo behavior by setting the

following flags in the OCITransCommit() function within your application:

■OCI_TRANS_WRITEBATCH

■OCI_TRANS_WRITENOWAIT

■OCI_TRANS_WRITEIMMED

■OCI_TRANS_WRITEWAIT

Note that the specification of the NOWAIT and BATCH options allows a small window

of vulnerability in which Oracle Database can roll back a transaction that your

application view as committed. Your application must be able to tolerate the following

scenarios:

■The database host crashes, which causes the database to lose redo that was

buffered but not yet written to the online redo logs.

■A file I/O problem prevents log writer from writing buffered redo to disk. If the

redo logs are not multiplexed, then the commit is lost.

Rolling Back Transactions

To roll back an entire transaction, or to roll back part of a transaction to a savepoint,

use the ROLLBACK statement. For example, either of the following statements rolls

back the entire current transaction:

ROLLBACK WORK;

ROLLBACK;

The WORK option of the ROLLBACK command has no function.

To roll back to a savepoint defined in the current transaction, use the TO option of the

ROLLBACK command. For example, either of the following statements rolls back the

current transaction to the savepoint named POINT1:

SAVEPOINT Point1;

...

Note: You cannot change the default IMMEDIATE and WAIT behavior

for distributed transactions.

See Also:

■Oracle Database SQL Reference for information on the COMMIT

statement

■Oracle Call Interface Programmer's Guide for information about the

OCITransCommit() function

Ensuring Repeatable Reads with Read-Only Transactions

SQL Processing for Application Developers 2-5

ROLLBACK TO SAVEPOINT Point1;

ROLLBACK TO Point1;

Defining Transaction Savepoints

To define a savepoint in a transaction, use the SAVEPOINT command. The following

statement creates the savepoint named ADD_EMP1 in the current transaction:

SAVEPOINT Add_emp1;

If you create a second savepoint with the same identifier as an earlier savepoint, the

earlier savepoint is erased. After creating a savepoint, you can roll back to the

savepoint.

There is no limit on the number of active savepoints for each session. An active

savepoint is one that has been specified since the last commit or rollback.

An Example of COMMIT, SAVEPOINT, and ROLLBACK

Table 2–4 shows a series of SQL statements that illustrates the use of COMMIT,

SAVEPOINT, and ROLLBACK statements within a transaction.

Ensuring Repeatable Reads with Read-Only Transactions

By default, the consistency model for Oracle Database guarantees statement-level read

consistency, but does not guarantee transaction-level read consistency (repeatable

reads). If you want transaction-level read consistency, and if your transaction does not

require updates, then you can specify a read-only transaction. After indicating that your

transaction is read-only, you can execute as many queries as you like against any

database table, knowing that the results of each query in the read-only transaction are

consistent with respect to a single point in time.

A read-only transaction does not acquire any additional data locks to provide

transaction-level read consistency. The multi-version consistency model used for

Table 2–2 Use of COMMIT, SAVEPOINT, and ROLLBACK

SQL Statement Results

SAVEPOINT a; First savepoint of this transaction

DELETE...; First DML statement of this transaction

SAVEPOINT b; Second savepoint of this transaction

INSERT INTO...; Second DML statement of this transaction

SAVEPOINT c; Third savepoint of this transaction

UPDATE...; Third DML statement of this transaction.

ROLLBACK TO c; UPDATE statement is rolled back, savepoint C remains defined

ROLLBACK TO b; INSERT statement is rolled back, savepoint C is lost, savepoint B remains

defined

ROLLBACK TO c; ORA-01086 error; savepoint C no longer defined

INSERT INTO...; New DML statement in this transaction

COMMIT; Commits all actions performed by the first DML statement (the DELETE

statement) and the last DML statement (the second INSERT statement)

All other statements (the second and the third statements) of the

transaction were rolled back before the COMMIT. The savepoint A is no

longer active.

Using Cursors within Applications

2-6 Oracle Database Application Developer’s Guide - Fundamentals

statement-level read consistency is used to provide transaction-level read consistency;

all queries return information with respect to the system change number (SCN)

determined when the read-only transaction begins. Because no data locks are acquired,

other transactions can query and update data being queried concurrently by a

read-only transaction.

Long-running queries sometimes fail because undo information required for consistent

read operations is no longer available. This happens when committed undo blocks are

overwritten by active transactions. Automatic undo management provides a way to

explicitly control when undo space can be reused; that is, how long undo information

is retained. Your database administrator can specify a retention period by using the

parameter UNDO_RETENTION.

For example, if UNDO_RETENTION is set to 30 minutes, then all committed undo

information in the system is retained for at least 30 minutes. This ensures that all

queries running for 30 minutes or less, under usual circumstances, do not encounter

the OER error, "snapshot too old."

A read-only transaction is started with a SET TRANSACTION statement that includes

the READ ONLY option. For example:

SET TRANSACTION READ ONLY;

The SET TRANSACTION statement must be the first statement of a new transaction; if

any DML statements (including queries) or other non-DDL statements (such as SET

ROLE) precede a SET TRANSACTION READ ONLY statement, an error is returned. Once

a SET TRANSACTION READ ONLY statement successfully executes, only SELECT

(without a FOR UPDATE clause), COMMIT, ROLLBACK, or non-DML statements (such

as SET ROLE, ALTER SYSTEM, LOCK TABLE) are allowed in the transaction.

Otherwise, an error is returned. A COMMIT, ROLLBACK, or DDL statement terminates

the read-only transaction; a DDL statement causes an implicit commit of the read-only

transaction and commits in its own transaction.

Using Cursors within Applications

PL/SQL implicitly declares a cursor for all SQL data manipulation statements,

including queries that return only one row. For queries that return more than one row,

you can explicitly declare a cursor to process the rows individually.

A cursor is a handle to a specific private SQL area. In other words, a cursor can be

thought of as a name for a specific private SQL area. A PL/SQL cursor variable

enables the retrieval of multiple rows from a stored procedure. Cursor variables allow

you to pass cursors as parameters in your 3GL application. Cursor variables are

described in Oracle Database PL/SQL User's Guide and Reference.

Although most Oracle Database users rely on the automatic cursor handling of the

database utilities, the programmatic interfaces offer application designers more control

over cursors. In application development, a cursor is a named resource available to a

program, which can be specifically used for parsing SQL statements embedded within

the application.

Declaring and Opening Cursors

There is no absolute limit to the total number of cursors one session can have open at

one time, subject to two constraints:

See Also: Oracle Database Administrator's Guide for information on

long-running queries and resumable space allocation

Using Cursors within Applications

SQL Processing for Application Developers 2-7

■Each cursor requires virtual memory, so a session's total number of cursors is

limited by the memory available to that process.

■A systemwide limit of cursors for each session is set by the initialization parameter

named OPEN_CURSORS found in the parameter file (such as INIT.ORA).

Explicitly creating cursors for precompiler programs can offer some advantages in

tuning those applications. For example, increasing the number of cursors can often

reduce the frequency of parsing and improve performance. If you know how many

cursors may be required at a given time, then you can make sure you can open that

many simultaneously.

Using a Cursor to Execute Statements Again

After each stage of execution, the cursor retains enough information about the SQL

statement to reexecute the statement without starting over, as long as no other SQL

statement has been associated with that cursor. The statement can be reexecuted

without including the parse stage.

By opening several cursors, the parsed representation of several SQL statements can

be saved. Repeated execution of the same SQL statements can thus begin at the

describe, define, bind, or execute step, saving the repeated cost of opening cursors and

parsing.

To understand the performance characteristics of a cursor, a DBA can retrieve the text

of the query represented by the cursor using the V$SQL catalog view. Because the

results of EXPLAIN PLAN on the original query might differ from the way the query is

actually processed, a DBA can get more precise information by examining the

V$SQL_PLAN, V$SQL_PLAN_STATISTICS, and V$SQL_PLAN_STATISTICS_ALL

catalog views.:

■The V$SQL_PLAN view contains the execution plan information for each child

cursor loaded in the library cache.

■The V$SQL_PLAN_STATISTICS view provides execution statistics at the row

source level for each child cursor.

■The V$SQL_PLAN_STATISTICS_ALL view contains memory usage statistics for

row sources that use SQL memory (sort or hash-join). This view concatenates

information in V$SQL_PLAN with execution statistics from

V$SQL_PLAN_STATISTICS and V$SQL_WORKAREA.

Closing Cursors

Closing a cursor means that the information currently in the associated private area is

lost and its memory is deallocated. Once a cursor is opened, it is not closed until one of

the following events occurs:

■The user program terminates its connection to the server.

■If the user program is an OCI program or precompiler application, then it

explicitly closes any open cursor during the execution of that program. (However,

when this program terminates, any cursors remaining open are implicitly closed.)

See Also: Oracle Database Reference for descriptions of parameters

See Also: Oracle Database Reference for details on these views

Locking Data Explicitly

2-8 Oracle Database Application Developer’s Guide - Fundamentals

Cancelling Cursors

Cancelling a cursor frees resources from the current fetch.The information currently in

the associated private area is lost but the cursor remains open, parsed, and associated

with its bind variables.

Locking Data Explicitly

Oracle Database always performs necessary locking to ensure data concurrency,

integrity, and statement-level read consistency. You can override these default locking

mechanisms. For example, you might want to override the default locking of Oracle

Database if:

■You want transaction-level read consistency or "repeatable reads"—where

transactions query a consistent set of data for the duration of the transaction,

knowing that the data has not been changed by any other transactions. This level

of consistency can be achieved by using explicit locking, read-only transactions,

serializable transactions, or overriding default locking for the system.

■A transaction requires exclusive access to a resource. To proceed with its

statements, the transaction with exclusive access to a resource does not have to

wait for other transactions to complete.

The automatic locking mechanisms can be overridden at the transaction level.

Transactions including the following SQL commands override Oracle Database's

default locking:

■LOCK TABLE

■SELECT, including the FOR UPDATE clause

■SET TRANSACTION with the READ ONLY or ISOLATION LEVEL SERIALIZABLE

options

Locks acquired by these statements are released after the transaction is committed or

rolled back.

The following sections describe each option available for overriding the default

locking of Oracle Database. The initialization parameter DML_LOCKS determines the

maximum number of DML locks allowed.

Although the default value is usually enough, you might need to increase it if you use

additional manual locks.

Note: You cannot cancel cursors using Pro*C/C++ or PL/SQL.

See Also: Oracle Call Interface Programmer's Guide for more

information about cancelling cursors

See Also: Oracle Database Reference for a discussion of parameters

Caution: If you override the default locking of Oracle Database at

any level, be sure that the overriding locking procedures operate

correctly: Ensure that data integrity is guaranteed, data concurrency is

acceptable, and deadlocks are not possible or are appropriately

handled.

Locking Data Explicitly

SQL Processing for Application Developers 2-9

Choosing a Locking Strategy

A transaction explicitly acquires the specified table locks when a LOCK TABLE

statement is executed. A LOCK TABLE statement manually overrides default locking.

When a LOCK TABLE statement is issued on a view, the underlying base tables are

locked. The following statement acquires exclusive table locks for the EMP_TAB and

DEPT_TAB tables on behalf of the containing transaction:

LOCK TABLE Emp_tab, Dept_tab

IN EXCLUSIVE MODE NOWAIT;

You can specify several tables or views to lock in the same mode; however, only a

single lock mode can be specified for each LOCK TABLE statement.

You can also indicate if you do or do not want to wait to acquire the lock. If you

specify the NOWAIT option, then you only acquire the table lock if it is immediately

available. Otherwise an error is returned to notify that the lock is not available at this

time. In this case, you can attempt to lock the resource at a later time. If NOWAIT is

omitted, then the transaction does not proceed until the requested table lock is

acquired. If the wait for a table lock is excessive, then you might want to cancel the

lock operation and retry at a later time; you can code this logic into your applications.

When to Lock with ROW SHARE and ROW EXCLUSIVE Mode

LOCK TABLE Emp_tab IN ROW SHARE MODE;

LOCK TABLE Emp_tab IN ROW EXCLUSIVE MODE;

ROW SHARE and ROW EXCLUSIVE table locks offer the highest degree of concurrency.

You might use these locks if:

■Your transaction needs to prevent another transaction from acquiring an

intervening share, share row, or exclusive table lock for a table before the table can

be updated in your transaction. If another transaction acquires an intervening

share, share row, or exclusive table lock, no other transactions can update the table

until the locking transaction commits or rolls back.

■Your transaction needs to prevent a table from being altered or dropped before the

table can be modified later in your transaction.

When to Lock with SHARE Mode

LOCK TABLE Emp_tab IN SHARE MODE;

SHARE table locks are rather restrictive data locks. You might use these locks if:

■Your transaction only queries the table, and requires a consistent set of the table

data for the duration of the transaction.

■You can hold up other transactions that try to update the locked table, until all

transactions that hold SHARE locks on the table either commit or roll back.

■Other transactions may acquire concurrent SHARE table locks on the same table,

also allowing them the option of transaction-level read consistency.

Note: When a table is locked, all rows of the table are locked. No

other user can modify the table.

Locking Data Explicitly

2-10 Oracle Database Application Developer’s Guide - Fundamentals

For example, assume that two tables, EMP_TAB and BUDGET_TAB, require a consistent

set of data in a third table, DEPT_TAB. For a given department number, you want to

update the information in both of these tables, and ensure that no new members are

added to the department between these two transactions.

Although this scenario is quite rare, it can be accommodated by locking the DEPT_TAB

table in SHARE MODE, as shown in the following example. Because the DEPT_TAB table

is rarely updated, locking it probably does not cause many other transactions to wait

long.

LOCK TABLE Dept_tab IN SHARE MODE;

UPDATE Emp_tab

SET sal = sal * 1.1

WHERE deptno IN

(SELECT deptno FROM Dept_tab WHERE loc = 'DALLAS');

UPDATE Budget_tab

SET Totsal = Totsal * 1.1

WHERE Deptno IN

(SELECT Deptno FROM Dept_tab WHERE Loc = 'DALLAS');

COMMIT; /* This releases the lock */

When to Lock with SHARE ROW EXCLUSIVE Mode

LOCK TABLE Emp_tab IN SHARE ROW EXCLUSIVE MODE;

Caution: Your transaction may or may not update the table later in

the same transaction. However, if multiple transactions concurrently

hold share table locks for the same table, no transaction can update

the table (even if row locks are held as the result of a SELECT... FOR

UPDATE statement). Therefore, if concurrent share table locks on the

same table are common, updates cannot proceed and deadlocks are

common. In this case, use share row exclusive or exclusive table locks

instead.

Note: You may need to set up data structures similar to the following

for certain examples to work:

CREATE TABLE dept_tab(

deptno NUMBER(2) NOT NULL,

dname VARCHAR2(14),

loc VARCHAR2(13));

CREATE TABLE emp_tab (

empno NUMBER(4) NOT NULL,

ename VARCHAR2(10),

job VARCHAR2(9),

mgr NUMBER(4),

hiredate DATE,

sal NUMBER(7,2),

comm NUMBER(7,2),

deptno NUMBER(2));

CREATE TABLE Budget_tab (

totsal NUMBER(7,2),

deptno NUMBER(2) NOT NULL);

Locking Data Explicitly

SQL Processing for Application Developers 2-11

You might use a SHARE ROW EXCLUSIVE table lock if:

■Your transaction requires both transaction-level read consistency for the specified

table and the ability to update the locked table.

■You do not care if other transactions acquire explicit row locks (using SELECT...

FOR UPDATE), which might make UPDATE and INSERT statements in the locking

transaction wait and might cause deadlocks.

■You only want a single transaction to have this behavior.

When to Lock in EXCLUSIVE Mode

LOCK TABLE Emp_tab IN EXCLUSIVE MODE;

You might use an EXCLUSIVE table if:

■Your transaction requires immediate update access to the locked table. When your

transaction holds an exclusive table lock, other transactions cannot lock specific

rows in the locked table.

■Your transaction also ensures transaction-level read consistency for the locked

table until the transaction is committed or rolled back.

■You are not concerned about low levels of data concurrency, making transactions

that request exclusive table locks wait in line to update the table sequentially.

Privileges Required

You can automatically acquire any type of table lock on tables in your schema. To

acquire a table lock on a table in another schema, you must have the LOCK ANY TABLE

system privilege or any object privilege (for example, SELECT or UPDATE) for the

table.

Letting Oracle Database Control Table Locking

Letting Oracle Database control table locking means your application needs less

programming logic, but also has less control, than if you manage the table locks

yourself.

Issuing the command SET TRANSACTION ISOLATION LEVEL SERIALIZABLE or

ALTER SESSION ISOLATION LEVEL SERIALIZABLE preserves ANSI serializability

without changing the underlying locking protocol. This technique allows concurrent

access to the table while providing ANSI serializability. Getting table locks greatly

reduces concurrency.

The settings for these parameters should be changed only when an instance is shut

down. If multiple instances are accessing a single database, then all instances should

use the same setting for these parameters.

See Also:

■Oracle Database SQL Reference for information on the SET

TRANSACTION statement

■Oracle Database SQL Reference for information on the ALTER

SESSION statements

Locking Data Explicitly

2-12 Oracle Database Application Developer’s Guide - Fundamentals

Explicitly Acquiring Row Locks

You can override default locking with a SELECT statement that includes the FOR

UPDATE clause. This statement acquires exclusive row locks for selected rows (as an

UPDATE statement does), in anticipation of updating the selected rows in a subsequent

statement.

You can use a SELECT... FOR UPDATE statement to lock a row without actually

changing it. For example, several triggers in Chapter 9, "Coding Triggers", show how

to implement referential integrity. In the EMP_DEPT_CHECK trigger (see "Foreign Key

Trigger for Child Table"), the row that contains the referenced parent key value is

locked to guarantee that it remains for the duration of the transaction; if the parent key

is updated or deleted, referential integrity would be violated.

SELECT... FOR UPDATE statements are often used by interactive programs that allow a

user to modify fields of one or more specific rows (which might take some time); row

locks are acquired so that only a single interactive program user is updating the rows

at any given time.

If a SELECT... FOR UPDATE statement is used when defining a cursor, the rows in the

return set are locked when the cursor is opened (before the first fetch) rather than

being locked as they are fetched from the cursor. Locks are only released when the

transaction that opened the cursor is committed or rolled back, not when the cursor is

closed.

Each row in the return set of a SELECT... FOR UPDATE statement is locked

individually; the SELECT... FOR UPDATE statement waits until the other transaction

releases the conflicting row lock. If a SELECT... FOR UPDATE statement locks many

rows in a table, and if the table experiences a lot of update activity, it might be faster to

acquire an EXCLUSIVE table lock instead.

When acquiring row locks with SELECT... FOR UPDATE, you can specify the NOWAIT

option to indicate that you are not willing to wait to acquire the lock. If you cannot

acquire then lock immediately, an error is returned to signal that the lock is not

possible at this time. You can try to lock the row again later.

By default, the transaction waits until the requested row lock is acquired. If the wait

for a row lock is too long, you can code logic into your application to cancel the lock

operation and try again later.

Note: The return set for a SELECT... FOR UPDATE may change

while the query is running; for example, if columns selected by the

query are updated or rows are deleted after the query started. When

this happens, SELECT... FOR UPDATE acquires locks on the rows

that did not change, gets a new read-consistent snapshot of the table

using these locks, and then restarts the query to acquire the remaining

locks.

This can cause a deadlock between sessions querying the table

concurrently with DML operations when rows are locked in a

non-sequential order. To prevent such deadlocks, design your

application so that any concurrent DML on the table does not affect

the return set of the query. If this is not feasible, you may want to

serialize queries in your application.

About User Locks

SQL Processing for Application Developers 2-13

About User Locks

You can use Oracle Lock Management services for your applications by making calls

to the DBMS_LOCK package. It is possible to request a lock of a specific mode, give it a

unique name recognizable in another procedure in the same or another instance,

change the lock mode, and release it. Because a reserved user lock is the same as an

Oracle Database lock, it has all the features of a database lock, such as deadlock

detection. Be certain that any user locks used in distributed transactions are released

upon COMMIT, or an undetected deadlock can occur.

When to Use User Locks

User locks can help to:

■Provide exclusive access to a device, such as a terminal

■Provide application-level enforcement of read locks

■Detect when a lock is released and cleanup after the application

■Synchronize applications and enforce sequential processing

Example of a User Lock

The following Pro*COBOL precompiler example shows how locks can be used to

ensure that there are no conflicts when multiple people need to access a single device.

*****************************************************************

* Print Check *

* Any cashier may issue a refund to a customer returning goods. *

* Refunds under $50 are given in cash, more than $50 by check. *

* This code prints the check. The one printer is opened by all *

* the cashiers to avoid the overhead of opening and closing it *

* for every check. This means that lines of output from multiple*

* cashiers could become interleaved if we don't ensure exclusive*

* access to the printer. The DBMS_LOCK package is used to *

* ensure exclusive access. *

*****************************************************************

CHECK-PRINT

* Get the lock "handle" for the printer lock.

MOVE "CHECKPRINT" TO LOCKNAME-ARR.

MOVE 10 TO LOCKNAME-LEN.

EXEC SQL EXECUTE

BEGIN DBMS_LOCK.ALLOCATE_UNIQUE ( :LOCKNAME, :LOCKHANDLE );

END; END-EXEC.

* Lock the printer in exclusive mode (default mode).

EXEC SQL EXECUTE

BEGIN DBMS_LOCK.REQUEST ( :LOCKHANDLE );

END; END-EXEC.

* We now have exclusive use of the printer, print the check.

...

* Unlock the printer so other people can use it

EXEC SQL EXECUTE

BEGIN DBMS_LOCK.RELEASE ( :LOCKHANDLE );

END; END-EXEC.

See Also: Oracle Database PL/SQL Packages and Types Reference for

detailed information on the DBMS_LOCK package

Using Serializable Transactions for Concurrency Control

2-14 Oracle Database Application Developer’s Guide - Fundamentals

Viewing and Monitoring Locks

Table 2–5 describes Oracle Database facilities to display locking information for

ongoing transactions within an instance.

Using Serializable Transactions for Concurrency Control

By default, Oracle Database permits concurrently executing transactions to modify,

add, or delete rows in the same table, and in the same data block. Changes made by

one transaction are not seen by another concurrent transaction until the transaction

that made the changes commits.

If a transaction A attempts to update or delete a row that has been locked by another

transaction B (by way of a DML or SELECT... FOR UPDATE statement), then A's DML

command blocks until B commits or rolls back. Once B commits, transaction A can see

changes that B has made to the database.

For most applications, this concurrency model is the appropriate one, because it

provides higher concurrency and thus better performance. But some rare cases require

transactions to be serializable. Serializable transactions must execute in such a way

that they appear to be executing one at a time (serially), rather than concurrently.

Concurrent transactions executing in serialized mode can only make database changes

that they could have made if the transactions ran one after the other.

Figure 2–1 shows a serializable transaction (B) interacting with another transaction

(A).

The ANSI/ISO SQL standard SQL92 defines three possible kinds of transaction

interaction, and four levels of isolation that provide increasing protection against these

interactions. These interactions and isolation levels are summarized in Table 2–4.

Table 2–3 Ways to Display Locking Information

Tool Description

Oracle Enterprise

Manager 10g Database

Control

From the Additional Monitoring Links section of the Database

Performance page, click Database Locks to display user blocks,

blocking locks, or the complete list of all database locks. Refer to

Oracle Database 2 Day DBA for more information.

UTLLOCKT.SQL The UTLLOCKT.SQL script displays a simple character lock wait-for

graph in tree structured fashion. Using any ad hoc SQL tool (such as

SQL*Plus) to execute the script, it prints the sessions in the system

that are waiting for locks and the corresponding blocking locks. The

location of this script file is operating system dependent. (You must

have run the CATBLOCK.SQL script before using UTLLOCKT.SQL.)

Table 2–4 Summary of ANSI Isolation Levels

Isolation Level Dirty Read1

1A transaction can read uncommitted data changed by another transaction.

Non-Repeatable Read2

2A transaction rereads data committed by another transaction and sees the new data.

Phantom Read3

3A transaction can execute a query again, and discover new rows inserted by another

committed transaction.

READ UNCOMMITTED Possible Possible Possible

READ COMMITTED Not possible Possible Possible

REPEATABLE READ Not possible Not possible Possible

SERIALIZABLE Not possible Not possible Not possible

Using Serializable Transactions for Concurrency Control

SQL Processing for Application Developers 2-15

The behavior of Oracle Database with respect to these isolation levels is summarized

in Table 2–5.

How Serializable Transactions Interact

Figure 2–1 on page 2-16 shows how a serializable transaction (Transaction B) interacts

with another transaction (A, which can be either SERIALIZABLE or READ

COMMITTED).

When a serializable transaction fails with an ORA-08177 error ("cannot serialize

access"), the application can take any of several actions:

■Commit the work executed to that point

■Execute additional, different, statements, perhaps after rolling back to a prior

savepoint in the transaction

■Roll back the entire transaction and try it again

Oracle Database stores control information in each data block to manage access by

concurrent transactions. To use the SERIALIZABLE isolation level, you must use the

INITRANS clause of the CREATE TABLE or ALTER TABLE command to set aside

storage for this control information. To use serializable mode, INITRANS must be set

to at least 3.

Table 2–5 ANSI Isolation Levels and Oracle Database

Isolation Level Description

READ UNCOMMITTED Oracle Database never permits "dirty reads." Although some other

database products use this undesirable technique to improve

thoughput, it is not required for high throughput with Oracle Database.

READ COMMITTED Oracle Database meets the READ COMMITTED isolation standard. This is

the default mode for all Oracle Database applications. Because an

Oracle Database query only sees data that was committed at the

beginning of the query (the snapshot time), Oracle Database actually

offers more consistency than is required by the ANSI/ISO SQL92

standards for READ COMMITTED isolation.

REPEATABLE READ Oracle Database does not normally support this isolation level, except

as provided by SERIALIZABLE.

SERIALIZABLE Oracle Database does not normally support this isolation level, except

as provided by SERIALIZABLE.

Using Serializable Transactions for Concurrency Control

2-16 Oracle Database Application Developer’s Guide - Fundamentals

Figure 2–1 Time Line for Two Transactions

Setting the Isolation Level of a Transaction

You can change the isolation level of a transaction using the ISOLATION LEVEL clause

of the SET TRANSACTION command, which must be the first command issued in a

transaction.

Use the ALTER SESSION command to set the transaction isolation level on a

session-wide basis.

The INITRANS Parameter

Oracle Database stores control information in each data block to manage access by

concurrent transactions. Therefore, if you set the transaction isolation level to

See Also: Oracle Database Reference for the complete syntax of the

SET TRANSACTION and ALTER SESSION commands

TRANSACTION A

(arbitrary)

begin work

update row 2

in block 1

Issue update "too recent"

for B to see

TIME

TRANSACTION B

(serializable)

SET TRANSACTION

ISOLATION LEVEL

SERIALIZABLE

read row 1 in block 1

Change other row in

same block, see own

changes

update row 1 in block 1

read updated row 1 in

block 1

insert row 4 Create possible

"phantom" row

Uncommitted changes

invisible

read old row 2 in block 1

search for row 4

(notfound)

commit

Make changes visible

to transactions that

begin later

Make changes

after A commits update row 3 in block 1

B can see its own changes

but not the committed

changes of transaction A.

re-read updated row 1

in block 1

search for row 4 (not found)

read old row 2 in block 1

Failure on attempt to update

row updated and committed

since transaction B began

update row 2 in block 1

FAILS; rollback and retry

Using Serializable Transactions for Concurrency Control

SQL Processing for Application Developers 2-17

SERIALIZABLE, then you must use the ALTER TABLE command to set INITRANS to

at least 3. This parameter causes Oracle Database to allocate sufficient storage in each

block to record the history of recent transactions that accessed the block. Higher values

should be used for tables that will undergo many transactions updating the same

blocks.

Referential Integrity and Serializable Transactions

Because Oracle Database does not use read locks, even in SERIALIZABLE

transactions, data read by one transaction can be overwritten by another. Transactions

that perform database consistency checks at the application level should not assume

that the data they read will not change during the execution of the transaction (even

though such changes are not visible to the transaction). Database inconsistencies can

result unless such application-level consistency checks are coded carefully, even when

using SERIALIZABLE transactions. Note, however, that the examples shown in this

section are applicable for both READ COMMITTED and SERIALIZABLE transactions.

Figure 2–2 on page 2-17 shows two different transactions that perform

application-level checks to maintain the referential integrity parent/child relationship

between two tables. One transaction checks that a row with a specific primary key

value exists in the parent table before inserting corresponding child rows. The other

transaction checks to see that no corresponding detail rows exist before deleting a

parent row. In this case, both transactions assume (but do not ensure) that data they

read will not change before the transaction completes.

Figure 2–2 Referential Integrity Check

The read issued by transaction A does not prevent transaction B from deleting the

parent row, and transaction B's query for child rows does not prevent transaction A

from inserting child rows. This scenario leaves a child row in the database with no

corresponding parent row. This result occurs even if both A and B are SERIALIZABLE

transactions, because neither transaction prevents the other from making changes in

the data it reads to check consistency.

TRANSACTION A TRANSACTION B

read parent (it exists) read child rows (not found)

insert child row(s) delete parent

commit work commit work

A's query does

not prevent this

delete

B's query does

not prevent this

insert

Using Serializable Transactions for Concurrency Control

2-18 Oracle Database Application Developer’s Guide - Fundamentals

As this example shows, sometimes you must take steps to ensure that the data read by

one transaction is not concurrently written by another. This requires a greater degree

of transaction isolation than defined by SQL92 SERIALIZABLE mode.

Using SELECT FOR UPDATE

Fortunately, it is straightforward in Oracle Database to prevent the anomaly described:

■Transaction A can use SELECT FOR UPDATE to query and lock the parent row and

thereby prevent transaction B from deleting the row.

■Transaction B can prevent Transaction A from gaining access to the parent row by

reversing the order of its processing steps. Transaction B first deletes the parent

row, and then rolls back if its subsequent query detects the presence of

corresponding rows in the child table.

Referential integrity can also be enforced in Oracle Database using database triggers,

instead of a separate query as in Transaction A. For example, an INSERT into the child

table can fire a BEFORE INSERT row-level trigger to check for the corresponding

parent row. The trigger queries the parent table using SELECT FOR UPDATE, ensuring

that parent row (if it exists) remains in the database for the duration of the transaction

inserting the child row. If the corresponding parent row does not exist, the trigger

rejects the insert of the child row.

SQL statements issued by a database trigger execute in the context of the SQL

statement that caused the trigger to fire. All SQL statements executed within a trigger

see the database in the same state as the triggering statement. Thus, in a READ

COMMITTED transaction, the SQL statements in a trigger see the database as of the

beginning of the triggering statement execution, and in a transaction executing in

SERIALIZABLE mode, the SQL statements see the database as of the beginning of the

transaction. In either case, the use of SELECT FOR UPDATE by the trigger correctly

enforces referential integrity.

READ COMMITTED and SERIALIZABLE Isolation

Oracle Database gives you a choice of two transaction isolation levels with different

characteristics. Both the READ COMMITTED and SERIALIZABLE isolation levels

provide a high degree of consistency and concurrency. Both levels reduce contention,

and are designed for deploying real-world applications. The rest of this section

compares the two isolation modes and provides information helpful in choosing

between them.

Transaction Set Consistency

A useful way to describe the READ COMMITTED and SERIALIZABLE isolation levels in

Oracle Database is to consider:

■A collection of database tables (or any set of data)

■A sequence of reads of rows in those tables

■The set of transactions committed at any moment

An operation (a query or a transaction) is transaction set consistent if its read

operations all return data written by the same set of committed transactions. When an

operation is not transaction set consistent, some reads reflect the changes of one set of

transactions, and other reads reflect changes made by other transactions. Such an

operation sees the database in a state that reflects no single set of committed

transactions.

Using Serializable Transactions for Concurrency Control

SQL Processing for Application Developers 2-19

Oracle Database transactions executing in READ COMMITTED mode are transaction-set

consistent on an individual-statement basis, because all rows read by a query must be

committed before the query begins.

Oracle Database transactions executing in SERIALIZABLE mode are transaction set

consistent on an individual-transaction basis, because all statements in a

SERIALIZABLE transaction execute on an image of the database as of the beginning of

the transaction.

In other database systems, a single query run in READ COMMITTED mode provides

results that are not transaction set consistent. The query is not transaction set

consistent, because it may see only a subset of the changes made by another

transaction. For example, a join of a master table with a detail table could see a master

record inserted by another transaction, but not the corresponding details inserted by

that transaction, or vice versa. The READ COMMITTED mode avoids this problem, and

so provides a greater degree of consistency than read-locking systems.

In read-locking systems, at the cost of preventing concurrent updates, SQL92

REPEATABLE READ isolation provides transaction set consistency at the statement

level, but not at the transaction level. The absence of phantom protection means two

queries issued by the same transaction can see data committed by different sets of

other transactions. Only the throughput-limiting and deadlock-susceptible

SERIALIZABLE mode in these systems provides transaction set consistency at the

transaction level.

Comparison of READ COMMITTED and SERIALIZABLE Transactions

Table 2–6 summarizes key similarities and differences between READ COMMITTED and

SERIALIZABLE transactions.

Table 2–6 Read Committed Versus Serializable Transaction

Operation Read Committed Serializable

Dirty write Not Possible Not Possible

Dirty read Not Possible Not Possible

Non-repeatable read Possible Not Possible

Phantoms Possible Not Possible

Compliant with ANSI/ISO SQL 92 Yes Yes

Read snapshot time Statement Transaction

Transaction set consistency Statement level Transaction level

Row-level locking Yes Yes

Readers block writers No No

Writers block readers No No

Different-row writers block writers No No

Same-row writers block writers Yes Yes

Waits for blocking transaction Yes Yes

Subject to "can't serialize access" error No Yes

Error after blocking transaction aborts No No

Error after blocking transaction commits No Yes

Autonomous Transactions

2-20 Oracle Database Application Developer’s Guide - Fundamentals

Choosing an Isolation Level for Transactions

Choose an isolation level that is appropriate to the specific application and workload.

You might choose different isolation levels for different transactions. The choice

depends on performance and consistency needs, and consideration of application

coding requirements.

For environments with many concurrent users rapidly submitting transactions, you

must assess transaction performance against the expected transaction arrival rate and

response time demands, and choose an isolation level that provides the required

degree of consistency while performing well. Frequently, for high performance

environments, you must trade-off between consistency and concurrency (transaction

throughput).

Both Oracle Database isolation modes provide high levels of consistency and

concurrency (and performance) through the combination of row-level locking and

Oracle Database's multi-version concurrency control system. Because readers and

writers do not block one another in Oracle Database, while queries still see consistent

data, both READ COMMITTED and SERIALIZABLE isolation provide a high level of

concurrency for high performance, without the need for reading uncommitted ("dirty")

data.

READ COMMITTED isolation can provide considerably more concurrency with a

somewhat increased risk of inconsistent results (due to phantoms and non-repeatable

reads) for some transactions. The SERIALIZABLE isolation level provides somewhat

more consistency by protecting against phantoms and non-repeatable reads, and may

be important where a read/write transaction executes a query more than once.

However, SERIALIZABLE mode requires applications to check for the "can't serialize

access" error, and can significantly reduce throughput in an environment with many

concurrent transactions accessing the same data for update. Application logic that

checks database consistency must take into account the fact that reads do not block

writes in either mode.

Application Tips for Transactions

When a transaction runs in serializable mode, any attempt to change data that was

changed by another transaction since the beginning of the serializable transaction

causes an error:

ORA-08177: Can't serialize access for this transaction.

When you get this error, roll back the current transaction and execute it again. The

transaction gets a new transaction snapshot, and the operation is likely to succeed.

To minimize the performance overhead of rolling back transactions and executing

them again, try to put DML statements that might conflict with other concurrent

transactions near the beginning of your transaction.

Autonomous Transactions

This section gives a brief overview of autonomous transactions and what you can do

with them.

See Also: Oracle Database PL/SQL User's Guide and Reference and

Chapter 9, "Coding Triggers" for detailed information on autonomous

transactions

Autonomous Transactions

SQL Processing for Application Developers 2-21

At times, you may want to commit or roll back some changes to a table independently

of a primary transaction's final outcome. For example, in a stock purchase transaction,

you may want to commit a customer's information regardless of whether the overall

stock purchase actually goes through. Or, while running that same transaction, you

may want to log error messages to a debug table even if the overall transaction rolls

back. Autonomous transactions allow you to do such tasks.

An autonomous transaction (AT) is an independent transaction started by another

transaction, the main transaction (MT). It lets you suspend the main transaction, do

SQL operations, commit or roll back those operations, then resume the main

transaction.

An autonomous transaction executes within an autonomous scope. An autonomous

scope is a routine you mark with the pragma (compiler directive)

AUTONOMOUS_TRANSACTION. The pragma instructs the PL/SQL compiler to mark a

routine as autonomous (independent). In this context, the term routine includes:

■Top-level (not nested) anonymous PL/SQL blocks

■Local, standalone, and packaged functions and procedures

■Methods of a SQL object type

■PL/SQL triggers

Figure 2–3 shows how control flows from the main routine (MT) to an autonomous

routine (AT) and back again. As you can see, the autonomous routine can commit

more than one transaction (AT1 and AT2) before control returns to the main routine.

Figure 2–3 Transaction Control Flow

When you enter the executable section of an autonomous routine,