NULL

The NULL constant defines a non-value.

Syntax

NULL

Usage

NULL indicates a lack of value.

When comparing variables to NULL, use the IS NULL operator, not the equal operator.

If an element of an expression is null, the expression is evaluated to NULL.

Variables are initialized to NULL or to zero, according to their data type.

Empty character string literals ("") are equivalent to NULL.

Important: NULL cannot be used with the == equal comparison operation, you must use IS NULL. For more details, see the IF statement.

Example

MAIN
  DEFINE s CHAR(5)
  LET s = NULL
  DISPLAY "s IS NULL evaluates to:"
  IF s IS NULL THEN
    DISPLAY "TRUE"
  ELSE
    DISPLAY "FALSE"
  END IF
END MAIN