NULL
The NULL
constant is provided as the "nil"
value.
Syntax
NULL
Usage
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