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Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć260 minutes Lecture 20 minutes Practice 80 minutes Total Class Management Note: Files required for lesson are: DEMO: l20

Modularizing Programming with

Subprograms

20

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć2

60 minutes Lecture

20 minutes Practice

80 minutes Total

Class Management Note:

Files required for lesson are:

DEMO: l20proc.pls, l20func.pls

PRACTICE: p20proc.pls

Modularity allows you to break your code into manageable, well-defined logical units Each of these units in PL/SQL is called a program unit, or a subprogram PL/SQL has two types of subprograms called procedures and functions This lesson covers the structure of subprograms and how to invoke them.

At the end of this lesson, you should be able to

D Determine the types of program units and where to use them

D Explain the differences between and benefits of procedures and functions

D Develop subprograms

D Invoke subprograms from Procedure Builder

Class Management Note:

This lesson is designed to give students an overview of a subprogrambecause Procedure Builder can only store subprograms, not anonymousblocks Therefore, use this lesson as a high level overview, with the details

to follow in the next lessons

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć4

Program units are named PL/SQL blocks They fall into three main categories:

D Procedures to perform actions

D Functions to compute a value

D Packages to bundle logically related procedures and functions

Stored or Application Subprogram?

These program units can be created in a variety of environments, including

server-side stored subprograms or as application subprograms.

Concept Stored Subprogram Application Subprogram

Location Is in the database Is within the application

Executed From any database tool or

application

From only the application inwhich it was created

Availability By way of database security Independently of, and in

addition to, stored subprograms.Subprograms are composed of a number of sections:

D A header to name and type the block

D An optional declarative section to set up local identifiers

D An executable part to perform the actions

D An optional exception handling section to handle exceptions

For more information, see

PL/SQL User’s Guide and Reference, Release 2.3, “Subprograms.”

Class Management Note:

Packages and other PL/SQL constructs are covered in the Develop

Database Procedures course.

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć6

Creating a Subprogram

The following steps will assist you to create a subprogram

1. Select your environment

If using Procedure Builder, then select either the Program Units node or theDatabase Objects node and Stored Procedures Units subobject node

2. Write your syntax.

If using Procedure Builder, enter the syntax in the Program Unit Editor If usingSQL*Plus, write your code in a text editor as a script file

3. Compile your code

The source code is complied into p-code If using Procedure Builder, click theCompile button If using SQL*Plus, start your file at the SQL prompt

4. Invoke the successfully compiled procedure or function

Guidelines

D SQL*Plus is another development environment for writing and for initial testing

of a procedure, although you will need to test the procedure by invoking it from

an application

D The SQL commands issued to create a stored subprogram are CREATE

PROCEDURE or CREATE FUNCTION

D The SQL commands issued to remove a stored subprogram are DROP

PROCEDURE or DROP FUNCTION

D Use CREATE OR REPLACE PROCEDURE or CREATE OR REPLACE

FUNCTION so you do not have to issue a DROP statement

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć8

Creating a Procedure

Create a PL/SQL procedure to store a series of actions for later execution The

procedure can contain zero or more parameters, which are arguments that you listwhen calling the procedure

where: name is the procedure name, which adheres to the

standard Oracle naming rules

parameter is the parameter syntax shown below

pl/sql_block is the procedural body that defines the action

performed by the procedure

The parameter syntax is as follows.

Syntax

parameter_name [IN | OUT | IN OUT] datatype

[{:= | DEFAULT} expr]

where: parameter_name is the name of the parameter

datatype is the datatype of the parameter, without

constraints

expr is the value to initialize the parameter

Guidelines

D Start the PL/SQL block with the keyword IS

D Enter any local declarations between IS and BEGIN

When creating the procedure from Procedure Builder, the CREATE OR REPLACEportion of the syntax is implied Therefore, when creating the procedure from

SQL*Plus, begin the statement with CREATE OR REPLACE

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć10

Creating a Procedure continuedProcedural Parameters

Transfer values to and from the calling environment through parameters There are

two types that you use When declaring a procedure, the formal parameter is used to define the values used in the executable portion of the PL/SQL block The actual parameter, or argument, is referenced when invoking a subprogram.

Parameter Modes for Formal Parameters

Parameter Mode Description

OUT Must be specified

Returns a value from the procedure to the callingenvironment

Formal parameter acts as an uninitialized variable.Formal parameter cannot be assigned to anothervariable or to itself

Actual parameter must be a variable; it cannot be aconstant or expression

IN OUT Must be specified

Passes a value from the calling environment into theprocedure, and returns a possibly different value fromthe procedure to the calling environment

Formal parameter acts as an initialized variable

Formal parameter can be used as a normal variable; itcan be assigned to a value

Actual parameter must be a variable

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć12

Class Management Note:

DEMO: l20proc.pls

PURPOSE: Demonstrate how to use the Procedure Builder environment,including loading and compiling code from a text file

1 Make sure you are connected to the database

2 Select from the menu File Load and load the file

3 Show students the code and Interpreter line command

You will invoke this procedure later in the lesson

Creating a Procedure continued

Eliminate Unnecessary IN Arguments

D Where possible, derive values in the procedure, or use column default values

D Generate the primary key using a database sequence

D Record the username from the USER function

D Record the current date from the SYSDATE function

D Take advantage of business rules to compute input values automatically using aformula

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć14

Comparing Functions and Procedures

A procedure can contain a list of parameters, but does not have to return a value It isinvoked in place of a complete PL/SQL statement A function differs from a

procedure in two ways:

D You invoke the function as part of an expression.

D A function must return a value.

SQL Functions

There are both user-defined functions, covered in this lesson, and SQL functions Youare already familiar with SQL functions You call the function with actual parametersfrom within a SQL command, such as SELECT

Example Number Functions

SYSDATE current date and time

s_dept_id.NEXTVAL database sequence value

A procedure containing one OUT argument can be rewritten as a function containing

a RETURN statement

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć16

Creating a Function

Create a PL/SQL function to return a value to the calling environment You mustdeclare the RETURN datatype in the header section of the function definition, anddefine the value to be returned in the PL/SQL block You can also declare a list ofparameters to be passed into the function

where: name is the function name, which adheres to the

standard Oracle naming rules

parameter is the parameter syntax See the syntax in the

“Procedure” section of this lesson

datatype is the datatype of the value to be returned

pl/sql_block is the procedural body that defines the action

performed by the procedure

The RETURN Statement

Remember to include a RETURN statement in the PL/SQL block The function mustset the value of the return parameter and be of the same datatype specified in theRETURN clause of the function definition Multiple RETURN statements are

allowed, but only one will be executed by any one call Typically, the multiple

RETURN statements are within an IF statement

When creating the function from Procedure Builder, the CREATE OR REPLACEportion of the syntax is implied Therefore, when creating the function from

SQL*Plus, begin the statement with CREATE OR REPLACE

Class Management Note:

When creating a stored function in PL/SQL version 2.x, you can use either

IS or AS to begin you PL/SQL block Procedure Builder 1.5 uses PL/SQLversion 1.5 and does not support the use of the AS keyword

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć18

Class Management Note:

DEMO: l20func.pls

PURPOSE: Demonstrate how to use the Procedure Builder environment,including importing text from a text file

1 Click the Subprograms node

2 Click the Create button

3 Fill out the dialog box: name = tax, function type

4 Highlight all text

5 Import file l20func.pls into the Program Unit Editor.

6 Click the Compile button Note “Successfully Compiled”

7 Click the Close button

You will invoke this function later in the lesson

If using SQL*Plus, edit the file to include the words “CREATE OR

REPLACE” Start the file at the SQL*Plus command prompt to compile

Creating a Function continued

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć20

Invoking Subprograms

You can call procedures and functions from any tool or language that supports

PL/SQL From PL/SQL, you can call a procedure with a direct call, and call a

function as part of an expression

Invoking Procedures from Procedure Builder

Enter the procedure name with any actual parameters, if applicable, at the ProcedureBuilder Interpreter prompt Procedure Builder then performs the action specified inthe procedure

Example

Use the CHANGE_SALARY procedure to change the salary to 1000 for employeenumber 17

PL/SQL> change_salary (17, 1000);

Note: You may want to confirm the changes by issuing a SELECT statement.

Invoking Procedures from Another Procedure

The example on the facing page illustrates how you can invoke a procedure fromanother procedure In the example, procedure CHANGE_SALARY is being invokedfrom procedure PROCESS_SAL Similarly, you can invoke a function from a storedprocedure or a PL/SQL anonymous block

To invoke procedures from SQL*Plus, use the EXECUTE command Use SQL*Plusbind variables to hold returned values You can also use SQL*Plus substitutionvariables through the ampersand (&) and variable name

Class Management Note:

DEMO

PURPOSE: Demonstrate invoking the CHANGE_SALARY procedure

1 At the Interpreter prompt, show the current salary for

employee 17 Enter: SELECT id, salary FROM s_emp

WHERE id = 17;

2 Enter: change_salary (17, 1000);

3 To show that the salary was updated,

enter: SELECT id, salary FROM s_emp WHERE id = 17;

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć22

Class Management Note:

DEMO

PURPOSE: Demonstrate invoking the standalone TAX function

1 Create the variable to hold the return value of the function

At the Interpreter prompt,

enter: .CREATE NUMBER x PRECISION 4

Invoking Subprograms continuedInvoking Standalone Functions

You can invoke a standalone function created in Procedure Builder First, you mustcreate a variable called the “identifier” to hold the returned value

Syntax

CREATE variable

where: variable is one of the following:

NUMBER var_name Specifies a variable, var_name, of the datatype [PRECISION number] NUMBER PRECISION determines the

[SCALE number] maximum number of objects SCALE

determines where rounding should occur

DATE var_name Specifies a variable, var_name, of the datatype

Display the tax based on a value Use the TAX function created earlier

PL/SQL> CREATE NUMBER x PRECISION 4

PL/SQL> :x := tax(100);

PL/SQL> TEXT_IO.PUT_LINE (TO_CHAR(:x));

7

For more information, see

Procedure Builder Developer’s Guide, “Working with PL/SQL Constructs.”

Note: To invoke functions from SQL*Plus, use the EXECUTE command Use

SQL*Plus global variables to hold returned values You can also use

SQL*Plus substitution variables through the ampersand (&) and variablename To view the result, use the SQL*Plus PRINT command

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć24

Class Management Note:

Actual parameters to a PL/SQL function called from a SQL statement mustuse the positional notation for parameters

Invoking Subprograms continuedInvoking Functions in SQL Statements

You can also call functions in SQL expressions Anywhere a built-in SQL functioncan be placed, a PL/SQL user-defined function can be placed as well

Advantages

D Permit calculations that are too complex, awkward, or unavailable with SQL

D Increase efficiency of queries by performing functions in the server rather than in

an application

Note: This feature is only available with PL/SQL 2.1 or higher and Oracle7 Server

release 7.1 or higher

Guidelines

D Only stored functions can be called from SQL statements, procedures cannot

D The function acts as a single-row function

D The function cannot contain a DML statement—the function cannot modifydatabase tables

D All formal parameters must be IN parameters; none can be an OUT or IN OUTparameter

D Datatypes used in the function must be Oracle7 Server internal datatypes, such asCHAR and DATE, not PL/SQL datatypes, such as BOOLEAN or RECORD

D The RETURN datatype must be an Oracle7 Server internal datatype

D You must own or have EXECUTE privileges on the PL/SQL function in order tocall it

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć26

Invoking Subprograms continuedCalling a Function

You can call functions from any of these SQL clauses

D The select list of a SELECT command

D The condition of a WHERE and HAVING clause

D The CONNECT BY, START WITH, ORDER BY, and GROUP BY clauses

D The VALUES clause of the INSERT command

D The SET clause of the UPDATE command

Example

Use the TAX function to calculate the tax on the total sale for order number 100

PL/SQL> SELECT total, tax(total)

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć28

D Subprograms fall into three main categories:

D Procedures to perform actions

D Functions to compute a value

D Packages to bundle logically related procedures and functions

D A function differs from a procedure in two ways:

D You invoke the function as part of an expression

D A function must return a value

D Procedure and function components:

D Header—To name and type the block

D Declarative—To set up local identifiers (optional)

D Executable—To perform the actions

D Exception handling—To handle exceptions (optional)

D Invoke subprograms from the Procedure Builder Interpreter prompt

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 20Ć30