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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
THEN
sequence_of_statements2;]
boolean_expression2
…
[ELSE
sequence_of_statements3;]
END IF;
LOOPS
Simple Loops
LOOP
sequence_of_statements;
END LOOP;
EXIT [WHEN
exit the loop
condition];
is used to
WHILE Loops
WHILE
condition
LOOP
sequence_of_statements;
END LOOP:
EXIT or EXIT WHEN
used to exit the loop
will also be
FOR Loops
FOR
loop_counter
IN [REVERSE]
LOOP
sequence_of_statements;
END LOOP:
low_bound
..
high_bound
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;
/
•
•