Preface

PL/SQL, Oracle's procedural extension of SQL, is an advanced fourth-generation programming language (4GL). It offers modern features such as data encapsulation, overloading, collection types, exception handling, and information hiding. PL/SQL also offers seamless SQL access, tight integration with the Oracle server and tools, portability, and security.

This guide explains all the concepts behind PL/SQL and illustrates every facet of the language. Good programming style is stressed throughout and supported by numerous examples. Using this guide, you learn PL/SQL quickly and efficiently.

This preface contains these topics:

Audience

Anyone developing PL/SQL-based applications for Oracle will benefit from reading this guide. Written especially for programmers, this comprehensive treatment of PL/SQL will also be of value to systems analysts, project managers, and others interested in database applications. To use this guide effectively, you need a working knowledge of Oracle, SQL, and a 3GL such as Ada, C, or COBOL.

You will not find installation instructions or system-specific information in this guide. For that kind of information, see the Oracle installation or user's guide for your system.

Organization

The PL/SQL User's Guide and Reference contains:

Chapter 1, "Overview of PL/SQL"

This chapter surveys the main features of PL/SQL and points out the advantages they offer. It also acquaints you with the basic concepts behind PL/SQL and the general appearance of PL/SQL programs.

Chapter 2, "Fundamentals of PL/SQL"

This chapter focuses on the small-scale aspects of PL/SQL. It discusses lexical units, scalar datatypes, user-defined subtypes, data conversion, expressions, assignments, block structure, declarations, and scope.

Chapter 3, "PL/SQL Datatypes"

This chapter discusses PL/SQL's predefined datatypes, which include integer, floating point, character, Boolean, date, collection, reference, and LOB types. It also discusses user-defined subtypes and data conversion.

Chapter 4, "PL/SQL Control Structures"

This chapter shows you how to structure the flow of control through a PL/SQL program. It describes conditional, iterative, and sequential control. You learn how to apply simple but powerful control structures such as IF-THEN-ELSE, CASE, and WHILE-LOOP.

Chapter 5, "PL/SQL Collections and Records"

This chapter focuses on the composite datatypes TABLE, VARRAY, and RECORD. You learn how to reference and manipulate whole collections of data, and how to treat related but dissimilar data as a logical unit. You also learn how to improve performance by bulk-binding collections.

Chapter 6, "Interaction Between PL/SQL and Oracle"

This chapter shows you how PL/SQL supports the SQL commands, functions, and operators that let you manipulate Oracle data. You also learn how to manage cursors, process transactions, and safeguard your database.

Chapter 7, "Handling PL/SQL Errors"

This chapter provides an in-depth discussion of error reporting and recovery. You learn how to detect and handle errors using PL/SQL exceptions.

Chapter 8, "PL/SQL Subprograms"

This chapter shows you how to write and use subprograms. It discusses procedures, functions, forward declarations, actual and formal parameters, positional and named notation, parameter modes, the NOCOPY compiler hint, parameter default values, aliasing, overloading, invoker rights, and recursion.

Chapter 9, "PL/SQL Packages"

This chapter shows you how to bundle related PL/SQL types, items, and subprograms into a package. Once written, your general-purpose package is compiled, then stored in an Oracle database, where its contents can be shared by many applications.

Chapter 10, "PL/SQL Object Types"

This chapter introduces you to object-oriented programming based on object types, which provide abstract templates for real-world objects. You learn how to define object types and manipulate objects.

Chapter 11, "Native Dynamic SQL"

This chapter shows you how to use dynamic SQL, an advanced programming technique that makes your applications more flexible and versatile. You learn two simple ways to write programs that can build and process SQL statements "on the fly" at run time.

Chapter 12, "Tuning PL/SQL Applications"

This chapter shows you how to tune PL/SQL-based applications. You learn how to make small adjustments that improve performance.

Chapter 13, "PL/SQL Language Elements"

This chapter uses syntax diagrams to show how commands, parameters, and other language elements are sequenced to form PL/SQL statements. Also, it provides usage notes and short examples to help you become fluent in PL/SQL quickly.

Appendix A, "Sample PL/SQL Programs"

This appendix provides several PL/SQL programs to guide you in writing your own. The sample programs illustrate important concepts and features.

Appendix B, "CHAR versus VARCHAR2 Semantics"

This appendix explains the subtle but important semantic differences between the CHAR and VARCHAR2 base types.

Appendix C, "PL/SQL Wrap Utility"

This appendix shows you how to run the Wrap Utility, a standalone programming utility that enables you to deliver PL/SQL applications without exposing your source code.

Appendix D, "PL/SQL Name Resolution"

Thus appendix explains how PL/SQL resolves references to names in potentially ambiguous SQL and procedural statements.

Appendix E, "PL/SQL Program Limits"

This appendix helps you deal with the program limits imposed by the PL/SQL compilation and run-time system.

Appendix F, "List of PL/SQL Reserved Words"

This appendix lists those words reserved for use by PL/SQL.

Conventions

This section describes the conventions used in the text and code examples of this documentation set. It describes:

Conventions in Text

We use various conventions in text to help you more quickly identify special terms. The following table describes those conventions and provides examples of their use.

Convention	Meaning	Example
Bold	Bold typeface indicates terms that are defined in the text or terms that appear in a glossary, or both.	When you specify this clause, you create an index-organized table.
Italics	Italic typeface indicates book titles or emphasis.	Oracle9i Database Concepts Ensure that the recovery catalog and target database do not reside on the same disk.
`UPPERCASE monospace (fixed-width font)`	Uppercase monospace typeface indicates elements supplied by the system. Such elements include parameters, privileges, datatypes, RMAN keywords, SQL keywords, SQL*Plus or utility commands, packages and methods, as well as system-supplied column names, database objects and structures, usernames, and roles.	You can specify this clause only for a `NUMBER` column. You can back up the database by using the `BACKUP` command. Query the `TABLE_NAME` column in the `USER_TABLES` data dictionary view. Use the `DBMS_STATS`.`GENERATE_STATS` procedure.
`lowercase monospace (fixed-width font)`	Lowercase monospace typeface indicates executables, filenames, directory names, and sample user-supplied elements. Such elements include computer and database names, net service names, and connect identifiers, as well as user-supplied database objects and structures, column names, packages and classes, usernames and roles, program units, and parameter values. Note: Some programmatic elements use a mixture of UPPERCASE and lowercase. Enter these elements as shown.	Enter `sqlplus` to open SQL*Plus. The password is specified in the `orapwd` file. Back up the datafiles and control files in the `/disk1/oracle/dbs` directory. The `department_id`, `department_name`, and `location_id` columns are in the `hr.departments` table. Set the `QUERY_REWRITE_ENABLED` initialization parameter to `true.` Connect as `oe` user. The `JRepUtil` class implements these methods.
`lowercase monospace (fixed-width font) italic`	Lowercase monospace italic font represents placeholders or variables.	You can specify the `parallel_clause`. Run `U``old_release``.SQL` where `old_release` refers to the release you installed prior to upgrading.

Conventions in Code Examples

Code examples illustrate SQL, PL/SQL, SQL*Plus, or other command-line statements. They are displayed in a monospace (fixed-width) font and separated from normal text as shown in this example:

SELECT username FROM dba_users WHERE username = 'MIGRATE';

The following table describes typographic conventions used in code examples and provides examples of their use.

Convention	Meaning	Example
[ ]	Brackets enclose one or more optional items. Do not enter the brackets.	`DECIMAL (``digits` `[ ,` `precision` `])`
{ }	Braces enclose two or more items, one of which is required. Do not enter the braces.	`{ENABLE \| DISABLE}`
\|	A vertical bar represents a choice of two or more options within brackets or braces. Enter one of the options. Do not enter the vertical bar.	`{ENABLE \| DISABLE}` `[COMPRESS \| NOCOMPRESS]`
`...`	Horizontal ellipsis points indicate either: That we have omitted parts of the code that are not directly related to the example That you can repeat a portion of the code	`CREATE TABLE ... AS` `subquery``;` `SELECT` `col1``,` `col2``, ... ,` `coln` `FROM employees;`
. . .	Vertical ellipsis points indicate that we have omitted several lines of code not directly related to the example.
Other notation	You must enter symbols other than brackets, braces, vertical bars, and ellipsis points as shown.	`acctbal NUMBER(11,2);` `acct CONSTANT NUMBER(4) := 3;`
`Italics`	Italicized text indicates placeholders or variables for which you must supply particular values.	`CONNECT SYSTEM/``system_password` `DB_NAME =` `database_name`
`UPPERCASE`	Uppercase typeface indicates elements supplied by the system. We show these terms in uppercase in order to distinguish them from terms you define. Unless terms appear in brackets, enter them in the order and with the spelling shown. However, because these terms are not case sensitive, you can enter them in lowercase.	`SELECT last_name, employee_id FROM employees;` `SELECT * FROM USER_TABLES;` `DROP TABLE hr.employees;`
`lowercase`	Lowercase typeface indicates programmatic elements that you supply. For example, lowercase indicates names of tables, columns, or files. Note: Some programmatic elements use a mixture of UPPERCASE and lowercase. Enter these elements as shown.	`SELECT last_name, employee_id FROM employees;` `sqlplus hr/hr` `CREATE USER mjones IDENTIFIED BY ty3MU9;`
`--`	A double hyphen begins a single-line comment, which extends to the end of a line.	`--`
`/* */`	A slash-asterisk and an asterisk-slash delimit a multi-line comment, which can span multiple lines.	`/* */`

Sample Database Tables

Most programming examples in this guide use two sample database tables named dept and emp. Their definitions follow:

CREATE TABLE dept (
   deptno NUMBER(2) NOT NULL,
   dname  VARCHAR2(14),
   loc    VARCHAR2(13));

CREATE TABLE emp (
   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));

Sample Data

Respectively, the dept and emp tables contain the following rows of data:

DEPTNO  DNAME      LOC
------- ---------- ---------
10      ACCOUNTING NEW YORK
20      RESEARCH   DALLAS
30      SALES      CHICAGO
40      OPERATIONS BOSTON

EMPNO ENAME   JOB          MGR  HIREDATE    SAL   COMM  DEPTNO
----- ------- --------- ------ --------- ------ ------ -------
 7369 SMITH   CLERK       7902 17-DEC-80    800             20
 7499 ALLEN   SALESMAN    7698 20-FEB-81   1600    300      30
 7521 WARD    SALESMAN    7698 22-FEB-81   1250    500      30
 7566 JONES   MANAGER     7839 02-APR-81   2975             20
 7654 MARTIN  SALESMAN    7698 28-SEP-81   1250   1400      30
 7698 BLAKE   MANAGER     7839 01-MAY-81   2850             30
 7782 CLARK   MANAGER     7839 09-JUN-81   2450             10
 7788 SCOTT   ANALYST     7566 19-APR-87   3000             20
 7839 KING    PRESIDENT        17-NOV-81   5000             10
 7844 TURNER  SALESMAN    7698 08-SEP-81   1500             30
 7876 ADAMS   CLERK       7788 23-MAY-87   1100             20
 7900 JAMES   CLERK       7698 03-DEC-81    950             30
 7902 FORD    ANALYST     7566 03-DEC-81   3000             20
 7934 MILLER  CLERK       7782 23-JAN-82   1300             10

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Accessibility of Code Examples in Documentation

JAWS, a Windows screen reader, 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, JAWS may not always read a line of text that consists solely of a bracket or brace.

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