IF Statement

The IF statement executes or skips a sequence of statements, depending on the value of a Boolean expression. For more information, see "Testing Conditions: IF and CASE Statements".

Syntax

if statement ::=

Description of the illustration if_statement.gif

Keyword and Parameter Description

boolean_expression

An expression that returns the Boolean value TRUE, FALSE, or NULL. Examples are comparisons for equality, greater-than, or less-than. The sequence following the THEN keyword is executed only if the expression returns TRUE.

ELSE

If control reaches this keyword, the sequence of statements that follows it is executed. This occurs when none of the previous conditional tests returned TRUE.

ELSIF

Introduces a Boolean expression that is evaluated if none of the preceding conditions returned TRUE.

THEN

If the expression returns TRUE, the statements after the THEN keyword are executed.

Usage Notes

There are three forms of IF statements: IF-THEN, IF-THEN-ELSE, and IF-THEN-ELSIF. The simplest form of IF statement associates a Boolean expression with a sequence of statements enclosed by the keywords THEN and END IF. The sequence of statements is executed only if the expression returns TRUE. If the expression returns FALSE or NULL, the IF statement does nothing. In either case, control passes to the next statement.

The second form of IF statement adds the keyword ELSE followed by an alternative sequence of statements. The sequence of statements in the ELSE clause is executed only if the Boolean expression returns FALSE or NULL. Thus, the ELSE clause ensures that a sequence of statements is executed.

The third form of IF statement uses the keyword ELSIF to introduce additional Boolean expressions. If the first expression returns FALSE or NULL, the ELSIF clause evaluates another expression. An IF statement can have any number of ELSIF clauses; the final ELSE clause is optional. Boolean expressions are evaluated one by one from top to bottom. If any expression returns TRUE, its associated sequence of statements is executed and control passes to the next statement. If all expressions return FALSE or NULL, the sequence in the ELSE clause is executed.

An IF statement never executes more than one sequence of statements because processing is complete after any sequence of statements is executed. However, the THEN and ELSE clauses can include more IF statements. That is, IF statements can be nested.

Examples

Example 13-3 shows an example of the IF-THEN-ELSIF-ELSE statement.

Example 13-3 Using the IF Statement

DECLARE
   jobid      employees.job_id%TYPE;
   empid      employees.employee_id%TYPE := 115;
   sal_raise  NUMBER(3,2);
BEGIN
  SELECT job_id INTO jobid from employees WHERE employee_id = empid;
  IF jobid = 'PU_CLERK' THEN sal_raise := .09;
  ELSIF jobid = 'SH_CLERK' THEN sal_raise := .08;
  ELSIF jobid = 'ST_CLERK' THEN sal_raise := .07;
  ELSE sal_raise := 0;
  END IF;
END;
/

For examples, see the following:

Example 1-7, "Using the IF-THEN_ELSE and CASE Statement for Conditional Control"
Example 4-1, "Using a Simple IF-THEN Statement"
Example 4-2, "Using a Simple IF-THEN-ELSE Statement"
Example 4-3, "Nested IF Statements"
Example 4-4, "Using the IF-THEN-ELSEIF Statement"