PL/SQL (Procedural Language extensions to SQL) Prepared by: Manoj Kathpalia Edited by: M V Ramakrishna

Outline Purpose of PL/SQL. PL/SQL block, its structure and types. PL/SQL Syntax.

Purpose of PL/SQL Procedural programming language used to access an Oracle database. Designed to overcome SQL's inability to handle control aspects of database interaction. Extends SQL by adding procedural language constructs, such as: - Variables and types.

- Control structures (IF-THEN-ELSE statements and loops). - Procedures and functions. Procedural constructs are integrated seamlessly with Oracle SQL, resulting in a structured, powerful language. Well-suited for designing complex applications.

PL/SQL Block Block is a basic unit in PL/SQL. All PL/SQL programs consist of blocks and each block performs a logical function in the program. Blocks can be nested within each other or can occur sequentially.

PL/SQL Block Structure DECLARE (Declarative section) BEGIN (Executable section) EXCEPTION (Exception handling section) END; / (/ at the end of a block tells Oracle to run the block)

Types of PL/SQL Blocks as Anonymous blocks which are compiled and run when loaded. as Triggers to maintain integrity. as Subprograms (Procedures and Functions) stored within the database that can be executed many times. as Packages, a named declarative section for storing related objects that can include procedures, functions and variables.

PL/SQL Syntax Declaration Variables are declared in the declarative section of the block. Variable declaration examples: v_student_id CHAR(8); v_lastname VARCHAR2(25); v_capacity NUMBER(3) := 200; ( := is used to initialize variables )

Types Basic PL/SQL types are: NUMBER(P,S) holds numeric value (where P is the precision and S is the scale) VARCHAR2(L) holds strings or character data (where L is the maximum length of the variable) CHAR(L) for fixed-length character strings DATE for storing date and time information BOOLEAN can hold TRUE, FALSE or NULL only

Declaring variables with %TYPE attribute %TYPE attribute is used when a PL/SQL variable is going to be used to manipulate the data stored in the database. The variable should have the same type as the table column (field). Specifying %TYPE attribute takes care.

For example, if the variable is used in the PL/SQL program to store the phone number of a student, following declaration can be used v_phone STUDENT.phone%TYPE; Instead of, say v_phone CHAR(10);

PL/SQL Syntax Control Structures IF-THEN-ELSE IF boolean_expression1 THEN sequence_of_statements1; [ELSIF boolean_expression2 THEN sequence_of_statements2; ] … [ELSE sequence_of_statements3; ] END IF;

LOOPS Simple Loops LOOP sequence_of_statements; END LOOP; EXIT [WHEN condition ]; is used to exit the loop

WHILE Loops WHILE condition LOOP sequence_of_statements; END LOOP: EXIT or EXIT WHEN will also be used to exit the loop

FOR Loops FOR loop_counter IN [REVERSE] low_bound.. high_bound LOOP sequence_of_statements; END LOOP:

Comments Single-line comments DECLARE v_title CHAR(2) -- title can be Mr or Ms … Multi-line comments DECLARE /* I am a multi-line comment */

-- Command to display the output at the SQL prompt SET SERVEROUTPUT ON -- This PL/SQL block accepts a number from the terminal, and prints out its square. -- You can try this from sql+ -- It has no exception handling code. DECLARE num1 NUMBER(3); num1_sq NUMBER(6); BEGIN -- prompts user for a value for 'anytemp' num1 := &anytemp; num1_sq := num1 * num1 ; DBMS_OUTPUT.PUT_LINE('THE SQUARE OF ' || num1 || ' IS ' || num1_sq); END; /