[Chapter 1] 1.6 Conditional and Sequential Control

1.6 Conditional and Sequential Control

PL/SQL includes conditional (IF) structures as well as sequential control (GOTO, NULL) constructs.

1.6.1 Conditional Control Statements

1.6.1.1 IF-THEN combination

IF condition THEN
   executable statement(s)
END IF;

For example:

IF caller_type = 'VIP' THEN
   generate_response('GOLD');
END IF;

1.6.1.2 IF-THEN-ELSE combination

IF condition THEN
   TRUE sequence_of_executable_statement(s)
ELSE
   FALSE/NULL sequence_of_executable_statement(s)
END IF;

For example:

IF caller_type = 'VIP' THEN
   generate_response('GOLD');
ELSE
   generate_response('BRONZE');
END IF;

1.6.1.3 IF-THEN-ELSIF combination

IF condition-1 THEN
   statements-1
ELSIF condition-N THEN
   statements-N
[ELSE
   else statements]
END IF;

For example:

IF caller_type = 'VIP' THEN
   generate_response('GOLD');
ELSIF priority_client THEN
   generate_response('SILVER');
ELSE
   generate_response('BRONZE');
END IF;

1.6.2 Sequential Control Statements

The GOTO statement performs unconditional branching to a named label. It should be used rarely. At least one executable statement must follow the label (the NULL statement can be this necessary executable statement). The format of a GOTO statement is:

GOTO label_name;

The format of the label is:

<< label_name >>

There are a number of scope restrictions on where a GOTO can branch control. A GOTO:

Can branch out of an IF statement, LOOP, or sub-block
Cannot branch into an IF statement, LOOP, or sub-block
Cannot branch from one section of an IF statement to another (from the IF/THEN section to the ELSE section is illegal)
Cannot branch into or out of a subprogram
Cannot branch from the exception section to the executable section of a PL/SQL block
Cannot branch from the executable section to the exception section of a PL/SQL block, although a RAISE does this

The NULL statement is an executable statement that does nothing. It is useful when an executable statement must follow a GOTO label or to aid readability in an IF-THEN-ELSE structure. For example:

IF :report.selection = 'DETAIL' THEN
   exec_detail_report;
ELSE
   NULL;
END IF;