Boolean operators

Operators AND, OR, and NOT combine Boolean values into a single Boolean expression:

Operators with AND, OR, and NOT return these results:

	left operand
right operand	result

AND

	TRUE	FALSE	NULL
TRUE	TRUE	FALSE	NULL
FALSE	FALSE	FALSE	FALSE
NULL	NULL	FALSE	NULL

For example, true AND false returns false.

OR

	TRUE	FALSE	NULL
TRUE	TRUE	TRUE	TRUE
FALSE	TRUE	FALSE	NULL
NULL	TRUE	NULL	NULL

For example, true OR false returns true.

NOT

TRUE	FALSE
FALSE	TRUE
NULL	NULL

For example, NOT false is true, and NOT null is null.

When one or both arguments are null, the result can also be null.

For example, if bool1 = TRUE and bool2 = NULL, bool1 AND bool2 returns NULL:

MAIN

Obtained results:

4gl tries to evaluate both operands of AND and OR logical operators, even if the value of the first operand has already determined the returned value. The NOT operator is recursive.