Control structures enable the program to change the logical flow of statements within PUS% with a number of control structures.
PL/SQL supports four basic programming control structures:
Conditional Control Statements
One can execute a statement sequence or sequence of
statements conditionally with the IF-THEN-ELSE statement. Sometimes it is
necessary to take alternative actions, depending on a condition or
circumstance.
The conditional controls are:
1) IF-THEN Statements: The simple form of the
conditional control statement is the IF-THEN statement.
Syntax:
IF condition THEN
statement(s)
END IF;
The statements that immediately follow the conditional IF
statement are executed only if the condition evaluates to True. If the
condition evaluates to False, the statements are not processed and are passed
over.
2) IF-THEN-ELSE Statements: The syntax of this type
of statement is shown below.
Syntax:
IF condition THEN
statement(s)
ELSE
statement(s)
END IF;
The statements that immediately follow the conditional IF
statement are executed only if the condition evaluates to True. If the
condition evaluates to False, the statements immediately following the ELSE
portion are executed. You can have nested IF-THEN-ELSE statements if You want.
3) IF-THEN-ELSEIF Statements: in some situations you
need to select an action from several mutually exclusive alternatives. The
IF-THEN-ELSEIF statement gives a solution for this. The IF-THEN-ELSEIF
statement enables you to have several mutually exclusive conditions.
Syntax:
IF condition1 THEN
statement(s);
ELSEIF condition2 THEN
statement(s);
ELSE
statement(s)
END IF;
This is how this structure works. PL/SQL evaluates the first
condition. If it is True, the statements following that are executed and the
control passes to the statement after the END IF. If condition) evaluates to
False, the ELSEIF clause is tested. If it is True the statements after it are
executed and control goes to statement after the END IF. If the condition2 is
found False, then control goes to the statements after the ELSE clause
