In this article, I describe How to use NULLIF in SQL server. As we know nullif clause used to checks the value is null or not. If the value is null then we define some default value.
SELECT ISNULL(NULLIF(Amount,''),0.00)FROM DBO.EMPLOYEE
In this above case, I am using isnull and nullif clause, first nullif clause check the amount is null or not .If it is null then return empty after that isnull clause will check whether the result is empty then return our default value.