Null Predicate

Function:

The NULL predicate tests a particular column to see if it contains the NULL value.

Invocation:

One of the six predicates which constitute a search term.

Syntax:

null_predicate.bmp

 

expression

May reference any valid column even if it does not support NULL values.  

NOT

Operator which negates the result of the predicate.

Description:

This predicate tests to see if a given expression evaluates to a NULL value. The NULL predicate can only return either true (column IS NULL) or false (column holds a definite value). The result can never be unknown.

Limitations:

None.

ANSI Specifics:

None.

CONNX Specifics:

None.

Example:

The following example determines if any cruises were offered for which no reservations have been made:

 

SELECT ID_CRUISE

    FROM CRUISE, CONTRACT

    WHERE CRUISE_ID = ID_CRUISE AND DATE_RESERVATION IS NULL;