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1 Copyright 2013, Oracle and/or its affiliates. All rightsreserved.

Database Programming with

PL/SQLUsing Conditional Compilation

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Objectives

This lesson covers the following objectives:

Describe the benefits of conditional compilation

Create and conditionally compile a PL/SQL programcontaining selection, inquiry, and error directives

Create and conditionally compile a PL/SQL programwhich calls the DBMS_DB_VERSIONserver-supplied

package

Using Conditional Compilation

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Purpose

Imagine you are creating a presentation as part of aschool project. You create it on your home PC usingMicrosoft Office 2007, which has some nice new

features such as 3-D graphics display.

When its finished, you will present your work to your

class at school, but until the day of the presentation

you wont know if the classroom PC will have Office2007 or an older version such as Office 2003, whichcant display 3-D graphics.


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Purpose (cont.)

You want to include 3-D graphics in your presentation,but you dont want it to fail while you are presenting to

your class. Conditional compilation can prevent an

embarrassing moment.


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What is Conditional Compilation?

Wouldnt it be great if you could somehow create your

PowerPoint presentation so that if you show it usingOffice 2007, the 3-D graphics are displayed, but if you

show it using Office 2003, the 2-D graphics aredisplayed instead?

That way, it wont fail regardless of the Office version

you use, and you automatically get the benefit of thenew features if theyre available.


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What is Conditional Compilation? (cont.)

You can do exactly this in PL/SQL by using ConditionalCompilation.


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reserved.

What is Conditional Compilation? (cont.)

Conditional Compilation allows you to include somesource code in your PL/SQL program that may becompiled or may be ignored (like a comment is

ignored), depending on the values of an initializationparameter, the version of the Oracle software you areusing, the value of a global package constant, or anyother condition that you choose to set.

You control conditional compilation by includingdirectivesin your source code. Directives are keywordsthat start with a single or double dollar sign ($ or $$).


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reserved.

Conditional Compilation and Microsoft Office

You cant really use PL/SQL with MS Office, so this is

not a real example, but lets pretend:

$IF,$THEN, $ELSE and$END are selection

directives.


CREATE OR REPLACE PROCEDURE lets_pretend IS

BEGIN...

$IF MS_OFFICE_VERSION >= '2007'$THENinclude_3_d_graphic;

$ELSE

include_2_d_graphic;

$END

...END lets_pretend;

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Conditional Compilation and Oracle Versions

You cant test which Office version youre using, but

youcan test which Oracle version youre using. This isa real subprogram:


CREATE OR REPLACE FUNCTION lets_be_real

RETURN NUMBER

$IF DBMS_DB_VERSION.VERSION >= 11 $THEN

DETERMINISTIC

$END

IS BEGIN

NULL; -- real source code here !

END lets_be_real;

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Conditional Compilation and Oracle Versions

(cont.)Deterministic functions are new in Oracle at Version11. This code includes the word DETERMINISTICif we

compile the function on Version 11 or later, and is

ignored if we compile on Version 10 or earlier.


CREATE OR REPLACE FUNCTION lets_be_real

RETURN NUMBER

$IF DBMS_DB_VERSION.VERSION >= 11 $THEN

DETERMINISTIC

$END

IS BEGINNULL; -- real source code here !

END lets_be_real;

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What is in the Data Dictionary Now?

After compiling the function on the previous slide, whatis stored in the Data Dictionary? USER_SOURCE

contains your complete source code, including the

compiler directives:


SELECT text FROM USER_SOURCE

WHERE type = 'FUNCTION' and name = 'LETS_BE_REAL'

ORDER BY line;

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Seeing Which Code has been Compiled

If you want to see which code has actually beenincluded in your compiled program, you use theDBMS_PREPROCESSOROracle-supplied package:

This function was compiled using Oracle Version 11:


BEGIN

DBMS_PREPROCESSOR.PRINT_POST_PROCESSED_SOURCE

('FUNCTION','','LETS_BE_REAL');

END;

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Using Selection Directives

There are five selection directives: $IF, $THEN,$ELSE, $ELSIFand $END(not $ENDIF). Their logic isthe same as IF, THEN, ELSEand so on, but they

control which code is included at compile time, notwhat happens at execution time.

Notice that $END does not end with a semicolon(;)unlike END;


...

$IF condition $THENstatement(s);

$ELSE statement(s);

$ELSIF statement(s);

$END

...

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Using Selection Directives Example

You have created a bodiless package that declares anumber of global constants:

Now, you want to create a subprogram that declaresan explicit cursor whose WHEREclause will depend on

the value of the Boolean package constant.


CREATE OR REPLACE PACKAGE tax_code_pack IS

new_tax_code CONSTANT BOOLEAN := TRUE; -- but could be FALSE...

END tax_code_pack;

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Using Selection Directives Example (cont.)

Now lets look at the contents of the Data Dictionary.Remember, the package set NEW_TAX_CODEto TRUE.


CREATE OR REPLACE PROCEDURE get_emps IS

CURSOR get_emps_curs ISSELECT * FROM employees

WHERE

$IF tax_code_pack.new_tax_code $THEN

salary > 20000;

$ELSE

salary > 50000;

$ENDBEGIN

FOR v_emps IN get_emps_curs LOOP

... /* real code here */

END LOOP;

END get_emps;

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Whats in the Data Dictionary?


SELECT text FROM USER_SOURCE

WHERE type = 'PROCEDURE' and name = 'GET_EMPS'

ORDER BY line;

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And what code was compiled?


BEGIN

DBMS_PREPROCESSOR.PRINT_POST_PROCESSED_SOURCE

('PROCEDURE','','GET_EMPS');

END;

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The PLSQL_CCFLAGSInitialization

ParameterYou may want to use the selection directives, such as$IF,to test for a condition that has nothing to do with

global package constants or Oracle software versions.

For example, you may want to include extra code tohelp you debug a PL/SQL program, but once the errorshave been corrected, you do not want to include this

code in the final version because it will slow down theperformance. You can control this using thePLSQL_CCFLAGSinitialization parameter.


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The PLSQL_CCFLAGSParameter (cont.)

PLSQL_CCFLAGSallows you to set values for

variables, and then test those variables in your PL/SQLprogram.

You define the variables and assign values to themusing PLSQL_CCFLAGS. Then, you test the values of

the variables in your PL/SQL program using inquiry

directives. An inquiry directive is the name of thevariable prefixed by a double dollar sign ($$).


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Using PLSQL_CCFLAGSand Inquiry

DirectivesFirst, set the value of the parameter:

Then compile your PL/SQL program:

After you have debugged the program, remove thedebugging code by:


ALTER SESSION SET PLSQL_CCFLAGS = 'debug:true';

CREATE OR REPLACE PROCEDURE testproc IS BEGIN

...

$IF $$debug $THEN

DBMS_OUTPUT.PUT_LINE('This code was executed');

$END

...

END testproc;

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Directives (cont.)After you have debugged the program, remove thedebugging code by:

and compile your procedure one more time to removethe debugging code.


ALTER SESSION SET PLSQL_CCFLAGS = 'debug:false';

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Directives (cont.)DEBUG is not a keyword: you can use any name youlike, and it can be a number or a character string, not

just a Boolean.


ALTER SESSION SET PLSQL_CCFLAGS = 'testflag:1';


...

$IF $$testflag > 0 $THEN

DBMS_OUTPUT.PUT_LINE('This code was executed');

$END

...

END testproc;

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Directives (cont.)You can set more than one variable, and then testthem either together or separately:


ALTER SESSION SET PLSQL_CCFLAGS =

'firstflag:1, secondflag:false';


...

$IF $$firstflag > 0 AND NOT $$secondflag $THEN

DBMS_OUTPUT.PUT_LINE('Testing both variables');

$ELSIF $$secondflag $THEN

DBMS_OUTPUT.PUT_LINE('Testing one variable');$END

...

END testproc;

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Directives (cont.)You can see which settings of PLSQL_CCFLAGSwere

used to compile a program by queryingUSER_PLSQL_OBJECT_SETTINGS.


SELECT name, plsql_ccflags

FROM USER_PLSQL_OBJECT_SETTINGS

WHERE name = 'TESTPROC';

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Directives (cont.)And, as always, you can see what was included in thecompiled program using DBMS_PREPROCESSOR.


BEGIN

DBMS_PREPROCESSOR.PRINT_POST_PROCESSED_SOURCE('PROCEDURE','','TESTPROC');

END;

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Using DBMS_DB_VERSION

DBMS_DB_VERSIONis a bodiless package that defines

a number of constants, including:

VERSION(the current Oracle software version)

VER_LE_11(= TRUE if the current Oracle softwareis version 11 or earlier)

VER_LE_10(= TRUE if the current Oracle software

is version 10 or earlier). So:

Is exactly the same as:


$IF DBMS_DB_VERSION.VER_LE_11 $THEN ...

$IF DBMS_DB_VERSION.VERSION

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Terminology

Key terms used in this lesson included:

Conditional compilation

DBMS_DB_VERSION

DBMS_PREPROCESSOR

Inquiry and selection directives

PLSQL_CCFLAGS


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28 Copyright 2013, Oracle and/or its affiliates. All rights

Summary

In this lesson, you should have learned how to:

Describe the benefits of conditional compilation

Create and conditionally compile a PL/SQL programcontaining selection, inquiry, and error directives

Create and conditionally compile a PL/SQL programwhich calls the DBMS_DB_VERSIONserver-supplied

package


PLSQL_s15_l03

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