Iterative Control Statements
Iterative control statements enable you to execute sequence
statements multiple times. The simplest form of an iterative statement in the
loop.
The iterative control statements are as follows:
1) Loop Statements: The syntax of the loop statement
is as shown below.
Syntax:
LOOP
statements(s)
END LOOP;
Each time the loop is processed, control is always resumed
at the top of the loop structure and statements are executed. The EXIT
statement provides a way to stop the iterative loop. The EXIT statement must be
placed inside the loop.
For example,
BEGIN
LOOP
count = count +1
IF count >=14 THEN
EXIT;
END IF;
END LOOP;
END;
2) F0R LOOP Statements: The FOR LOOP is a mechanism
to cycle through a loop fixed number of times. A FOR LOOP iterates over and
over for a specified number of times.
Syntax:
FOR counter IN lower bound ..
upper bound LOOP
statement(s)
END LOOP;
The range of valid integers for the counter is evaluated
when the loop is first entered and is never re-evaluated. After each iteration,
the counter is implicitly incremented. Also the counter is implicitly declared,
so you do not have to declare it. If the upper bound value is less than the
lower bound value the loop is never executed.
For example, following loop the statements will be
executed 30 times:
FOR k IN 1..30
LOOP
Statements
END LOOP;
3) LOOP Labels: In PUSQL, you may attach a label name
to a loop. This label, which is an undeclared identifier, must appear at the beginning
of the loop and must De enC IUS Optionally this label may be placed at the
without angle brackets.
For example, using labels to clearly mark the beginning
and of the looping structure:
« salary_loop>> -- loop label
FOR k IN 1..u_counter LOOP
UPDATE employee
SET salary = salary * 1.1;
END LOOP inventory_loop;
4) WHILE Statements: The WHILE-LOOP structure repeats
a statement until a condition is no longer true.
Syntax:
WHILE condition LOOP
statement(s)
END LOOP;
Before each iteration the condition is evaluated. If the
condition is True, the statements are executed. Otherwise the statements are
skipped and not executed.
For example,
DECLARE
counter NUMBER(2) : =1;
BEGIN
WHILE counter >20 LOOP
SELECT name INTO guest_name
FROM register
counter = counter +1 ;
END LOOP:
END:
