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Behavior of Null Values in Logical Expressions

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Null values persist through logical expressions in most cases. The following table describes the behavior of null values in logical expressions.

Logical

expression

Result if

x=TRUE

Result if

x=FALSE

Result if

x=.NULL.

x AND .NULL.

.NULL.

FALSE

.NULL.

x OR .NULL.

TRUE

.NULL.

.NULL.

NOT x

FALSE

TRUE

.NULL.

When a conditional expression encounters a null value, the condition fails, because .NULL. is not true (.T.). For example, a FOR clause that evaluates to .NULL. is treated as false (.F.). Note that null values are treated as .NULL. until the entire expression is evaluated.

See Also

Concepts

NULL as a Value

NULL as a Parameter

Reference

FOR Clauses

Null Value Handling

Behavior of Null Values in Commands and Functions

Other Resources

Data Manipulation