WHILE LOOP Statement

14.71 WHILE LOOP Statement

The WHILE LOOP statement runs one or more statements while a condition is TRUE.

Topics

The WHILE LOOP statement ends when the condition becomes FALSE or NULL, or when a statement inside the loop transfers control outside the loop or raises an exception.

Syntax

while_loop_statement ::=

Description of the illustration while_loop_statement.eps

( boolean_expression ::= , statement ::= )

Semantics

while_loop_statement

boolean_expression

Expression whose value is TRUE, FALSE, or NULL.

boolean_expression is evaluated at the beginning of each iteration of the loop. If its value is TRUE, the statements after LOOP run. Otherwise, control transfers to the statement after the WHILE LOOP statement.

statement

To prevent an infinite loop, at least one statement must change the value of boolean_expression to FALSE or NULL, transfer control outside the loop, or raise an exception. The statements that can transfer control outside the loop are:

"CONTINUE Statement" (when it transfers control to the next iteration of an enclosing labeled loop)
"EXIT Statement"
"GOTO Statement"
"RAISE Statement"

label

Label that identifies while_loop_statement (see "statement ::=" and "label"). CONTINUE, EXIT, and GOTO statements can reference this label.

Labels improve readability, especially when LOOP statements are nested, but only if you ensure that the label in the END LOOP statement matches a label at the beginning of the same LOOP statement (the compiler does not check).

Examples

Example 14-47 WHILE LOOP Statements

The statements in the first WHILE LOOP statement never run, and the statements in the second WHILE LOOP statement run once.

DECLARE
  done  BOOLEAN := FALSE;
BEGIN
  WHILE done LOOP
    DBMS_OUTPUT.PUT_LINE ('This line does not print.');
    done := TRUE;  -- This assignment is not made.
  END LOOP;

  WHILE NOT done LOOP
    DBMS_OUTPUT.PUT_LINE ('Hello, world!');
    done := TRUE;
  END LOOP;
END;
/

Result:

Hello, world!