Chapter 09 Creating Procedures 00

Objectives

After competing this lesson,you should be able to do the following:

• Identify the benefits of modualarized and layered subprogram design.
• Create and call procedures.
• Use formal and actual parameters
• Use positional,named ,or mixed notation for passing parameters.
• Identify the available parameter-passing modes.
• Handle exceptions in procedures.
• Remove a procedure
• Display the prcedures`s information.

Lesson Agenda

• Using a modularized and layered subprogram desing and identifying the benefits of subprograms.
• Working with procedures
  • -Creating and calling procedures
  • -Identifying the available parameter-passing modes
  • -Using formal and actual parameters
  • -Using positional,named,or mixed notation
• Handing execptions in procedures,removing a procedure,and displaying the procedures`s information.

Creating a Modularized Subprogram Desgin

Modularize code into subprograms.

1、Locate code sequences repeated more than onec.

2、Create subprogram P containing the repeated code.

3、Modify original code to invoke the new subprogram.

Creating a Layered Sumprogram Desgin

Create subprogram layers for you application.

• Data access subprogram layer with SQL logic.
• Business logic subprogram layer,which may or may not use the data access layer.

Modularizing Development with PL/SQL Blocks

• PL/SQL is a block-structed language.The PL/SQL code block helps modularize code by using:
  • -Anonymous blocks
  • -Procedures and Functions
  • -Packages
  • -Database triggers
• The benefits of using modular program constructs are:
  • -Easy maintenance
  • -Improved data security and integrity
  • -Improved performance
  • -Improved code clarity

Anonymous Blocks:Overview

Anonymous blocks:

• Form the basic PL/SQL block structure
• Initiate PL/SQL processing tasks from applications
• Can be nested within the executable section of any PL/SQL block.

[DECLARE        -- Declarationg Section (Optional)
        variable declarations;...]
BEGIN           --Executable Section(Mandatory)
        SQL or PL/SQL statements;
[EXCEPTION      --Exception Section (Optional)
        WHEN exception THEN statements;]
END;            --End of BLock(Mandatory)

PL/SQL Run-time Architecture

What Are PL/SQL Subprograms?

• A PL/SQL subprogram is a named PL/SQL block that can be called with a set fo prameters.
• You can declare and define a subprogram within either a PL/SQL block or another subprogram.
• A subprogram consists of a specification and a body
• A subprogram can be a procedure or a function.
• Typically,you use a procedure to perform an action and a fuction to compute and return a value.
• Subprograms can be grouped into PL/SQL packages.

The benefits of Using PL/SQL Subprograms

Differences Between Anonymous Blocks and Subprograms

Anonymous Blocks	Subprograms
Unnamed PL/SQL blocks	Named PL/SQL blocks
Compiled every time	Compiled only once
Not stored in the database	Stored in the database
Cannot be invoked  by other applicatons	Names and,therefore,can be invoked by other applicaitons
Do not return values	Subprograms called functions must return values.
Cannot take parameters	Can take parameters