Introduction to PL/SQL

N. Dimililer

About PL/SQL

– PL/SQL is an extension to SQL with design features of programming languages.

– Data manipulation and query statements of SQL are included within procedural units of code.

– PL/SQL offers modern software engineering features such as data encapsulation, exception handling, information hiding, and object orientation.

PL/SQL Blocks

Anonymous Block : Unnamed block of PL/SQL. These do not accept any parameters.

• Procedure : A series of statements accepting and/or returning zero or more variables through parameters.

• Function : A series of statements accepting zero or more variables that returns one value using an explicit RETURN statement.

• Package : A collection of procedures and functions that has two parts, a specification listing available procedures and functions and their parameters, and a body that contains the actual code for the procedures and functions.

• Trigger : A series of PL/SQL statements attached to a database table that execute whenever a triggering event (select, update, insert, delete) occurs.

Benefits of PL/SQL

• Integration

• Improved Performance

• Modularize Program Development

• Portability

• Identifiers can be used

• Procedural Language Control Structures

• Exception/Error handling

PL/SQL improves performance

ApplicationApplication Other DBMSsOther DBMSs

ApplicationApplicationOracle with

PL/SQLOracle with

PL/SQL

SQLSQL

SQLSQLSQLSQL

SQLSQL

SQLSQLIF...THENIF...THEN

SQLSQLELSEELSE

SQLSQLEND IF;END IF;SQLSQL

PL/SQL Block Structure

DECLAREDECLARE

BEGINBEGIN

EXCEPTIONEXCEPTION

END;END;

PL/SQL Block Structure

DECLAREDECLARE --optional --optional

BEGINBEGIN --mandatory --mandatory

EXCEPTIONEXCEPTION --optional --optional

END;END;

Variables, cursors, user-defined exceptions

SQL statementsPL/SQL statements

Actions to perform whenerrors occur

Executing Statements and PL/SQL Blocks from SQL*Plus

• Place a semicolon (;) at the end of a SQL statement or PL/SQL control statement.

• Use a slash (/) to run the anonymous PL/SQL block in the SQL*Plus buffer. When the block is executed successfully, without unhandled errors or compile errors, the message output should be as follows:

PL/SQL procedure successfully completed.

• Place a period (.) to close a SQL*Plus buffer. A PL/SQL block is treated as one continuous statement in the buffer, and the semicolons within the block do not close or run the buffer.

PL/SQL statements and semicolon

• In PL/SQL, an error is called an exception.• Section keywords DECLARE, BEGIN, and

EXCEPTION are not followed by semicolons.

• END and all other PL/SQL statements requirerequire a semicolon to terminate the statement.

• You can string statements together on the same line, but this method is not recommended for clarity or editing.

Use of Variables

• With PL/SQL you can declare variables and then use them in SQL and procedural statements anywhere an expression can be used.– Temporary storage of data– Manipulation of stored values– Reusability.– Ease of maintenance

Handling Variables in PL/SQL

– Declare and initialize variables in the declaration section.

– Assign new values to variables in the executable section.

– Pass values into PL/SQL blocks through parameters.(will be covered later on when we talk about procedures and functions)

– View results through output variables.– Remember: Uninitialized variables contain

“NULL” value

identifier [CONSTANT] datatype [NOT NULL] [:= | DEFAULT expr];

identifier [CONSTANT] datatype [NOT NULL] [:= | DEFAULT expr];

Declare v_hiredate DATE; v_deptno NUMBER(2) NOT NULL := 10;

v_gender VARCHAR2(6) := 'FEMALE'; v_city VARCHAR2(10); c_comm CONSTANT NUMBER := 1400;

Declare v_hiredate DATE; v_deptno NUMBER(2) NOT NULL := 10;

v_gender VARCHAR2(6) := 'FEMALE'; v_city VARCHAR2(10); c_comm CONSTANT NUMBER := 1400;

Declaration of PL/SQL variables

Syntax of declaration

Example declarationsYou cannot assign NULL to v_deptno. Must be initialized

The value of c_comm cannot be changed. Must be initialized at declaration

Assigning values to variables

v_ename := ‘Ali';v_ename := ‘Ali';

v_hiredate := '31-DEC-2012';v_hiredate := '31-DEC-2012';

identifier := expr;identifier := expr;

Set the employee name to “Ali”

Set v_hiredate to a date

Syntax of assignement

DBMS_OUTPUT.PUT_LINE

• Put_line is a procedure included in the Oracle-supplied package DBMS_OUTPUT

• Used for displaying data from a PL/SQL block on the screen

• Must be enabled in SQL*Plus with

SET SERVEROUTPUT ON

Example Anonymous Blocks

BEGIN

DBMS_OUTPUT.PUT_LINE(‘Hello world’);

END;

BEGIN

DBMS_OUTPUT.PUT_LINE(‘Today is’ || SYSDATE );

END;

Simply prints “Hello world”

on screen

Put_line accepts a single string as parameter. Use

concatenation operator if you have more than one string to

display

Example Anonymous Blocks

DECLARE

v_name varchar2(20);

BEGIN

v_name := ‘Ali’;

DBMS_OUTPUT.PUT_LINE(Hello || v_name);

END;

DECLARE

v_name varchar2(20) := ‘Ali’;

BEGIN

DBMS_OUTPUT.PUT_LINE(Hello || v_name);

END;

Variable InitializationVariable

declaration

v_name varchar2(20) DEFAULT ‘Ali’;

Task: Write an anonymous block to print “Hello Ali” on screen. Declare name as a variable

Variable declared and initialized at declaration

Example Anonymous Blocks

Read the name of user from keyboard and print “Hello <name>” on screen.

DECLARE

v_name varchar2(20);

BEGIN

v_name := &your_name;

DBMS_OUTPUT.PUT_LINE(‘Hello ’ || v_name);

END;

Enter value for your_name: ‘Veli’Old 4: v_name := &your_nameNew 4: v_name := ‘Veli’Hello Veli

Output

Substitution Variable: The value you enter from keyboard replaces the substitution variable Keyboard entry

Controlling Flow of Events

• You can change the logical flow of statements using conditional IF statements and loop control structures.

• Conditional IF statements:– IF-THEN-END IF– IF-THEN-ELSE-END IF– IF-THEN-ELSIF-ELSE-END IF

IF condition THEN statements;[ELSIF condition THEN statements;][ELSE statements;]END IF;

IF condition THEN statements;[ELSIF condition THEN statements;][ELSE statements;]END IF;

IF v_dept_name = ‘ITEC' THEN v_dept_no := 35;END IF;

IF v_dept_name = ‘ITEC' THEN v_dept_no := 35;END IF;

Syntax

Example: If v_dept_name is ‘ITEC’ change v_dept_no to 35.

IF STATEMENT

Example Anonymous Block

Task: Write an anonymous block that will print ‘weekend’ if the system date is ‘Sunday’ or ‘Saturday’.

DECLARE

v_current_date date := SYSDATE;

BEGIN

IF to_char(v_current_date, ‘d’) in (1,7) THEN

dbms_output.put_line(‘weekend’);

END IF;

END;

Example Anonymous Block

Task: Write an anonymous block that will print ‘weekend’ if the system date is ‘Sunday’ or ‘Saturday’ and ‘weekday’ otherwise.

BEGIN

IF to_char(sysdate, ‘d’) in (1,7) THEN

dbms_output.put_line(‘weekend’);

ELSE

dbms_output.put_line(‘weekday’);

END IF;

END;

Example Anonymous Block

Task: Write an anonymous block that will print weekend if the system date is ‘Sunday’ or ‘Saturday’, we have class if it is Tuesday or Thursday and no class otherwise.

BEGIN

IF to_char(sysdate, ‘d’) in (1,7) THEN

dbms_output.put_line(‘week end’);

ELSIF to_char(sysdate,’d’) in (3,5) THEN

dbms_output.put_line(‘we have class’);

ELSE

dbms_output.put_line(‘no class’);

END IF;

END;

Summary

• We learned the overall format of a PL/SQL anonymous block.

• If statement is covered.

• Next lesson we will learn about loops.