NULLIF Function in Oracle

NULLIF:

• The NULLIF function can be thought as null-if-equals function. 

• It compares two expressions. If they are equal server returns a null and If they not equal [or] if the second expression is null, the first expression is returned. 

• Both the compared expressions shall be source values.

SELECT NULLIF(22,22)FROM DUAL;

NULLIF(22,22)
-------------

SELECT NULLIF(22,23)FROM DUAL;
NULLIF(22,23)
-------------
           22

SELECT NULLIF(22,NULL)FROM DUAL;
NULLIF(22,NULL)
---------------
             22

SELECT NULLIF(NULL,NULL)FROM DUAL;
--IS WRONG