NULLIF( expression-1, expression-2 )

Data type of the first argument.

NULLIF compares the values of the two expressions.

If the first expression equals the second expression, NULLIF returns NULL.

If the first expression does not equal the second expression, or if the second expression is NULL, NULLIF returns the first expression.

The NULLIF function provides a short way to write some CASE expressions.

• CASE expressions

The following statement returns the value a:

SELECT NULLIF( 'a', 'b' );

The following statement returns NULL.

SELECT NULLIF( 'a', 'a' );