Behavior of Null Values in Logical Expressions

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.

Expand imageSee Also

© , 1996-2020 • Updated: 11/10/20
Comment or report problem with topic