Logical operators in DataWindow expressions

You use logical operators to combine boolean expressions into a larger boolean expression. The result is always true or false:

**Table 23-9: Using expressions with logical operators**
Operator	Meaning	Example
NOT	Logical negation. If A is true, NOT A is false. If A is false, NOT A is true.	NOT Price = 100
AND	Logical and. A AND B is true if both are true. A AND B is false if either is false.	Tax > 3 AND Ship < 5
OR	Logical or. A OR B is true if either is true or both are true. A OR B is false only if both are false.	Tax > 3 OR Ship < 5

When you combine two or more boolean expressions to form a new expression, the new expression is either true or false. The following truth table shows how true and false expressions are evaluated to form an expression that is either true or false.

For example, if “My dog has fleas” is true and “My hair is brown” is false, then “My dog has fleas OR my hair is brown” is true, and “My dog has fleas AND my hair is brown” is false:

**Table 23-10: Combining expressions with logical operators**
If one expression has this value	And the logical operator is	And if another expression has this value	The resulting expression has this value
TRUE	AND	TRUE	TRUE
TRUE	AND	FALSE	FALSE
FALSE	AND	TRUE	FALSE
FALSE	AND	FALSE	FALSE
TRUE	OR	TRUE	TRUE
TRUE	OR	FALSE	TRUE
FALSE	OR	TRUE	TRUE
FALSE	OR	FALSE	FALSE
NOT TRUE	AND	TRUE	FALSE
NOT TRUE	AND	FALSE	FALSE
NOT FALSE	AND	TRUE	TRUE
NOT FALSE	AND	FALSE	FALSE
NOT TRUE	OR	TRUE	TRUE
NOT TRUE	OR	FALSE	FALSE
NOT FALSE	OR	TRUE	TRUE
NOT FALSE	OR	FALSE	TRUE

If you use a logical operator with a boolean function that returns null, the term with the null return value is evaluated as false. If you use the NOT logical operator with a boolean function that returns null, the complete term evaluates to true. For example, NOT gf_boolean () evaluates to true when gf_boolean returns null.