It accepts the two values, if both the values are matched then it will return NULL otherwise it will return first value. Examples-1: Declare @FisrtName varchar ( 100 ), @LastName varchar ( 100 ) Set @FisrtName = 'Rakesh' Set @LastName = 'Rakesh' Select NULLIF ( @FisrtName , @LastName ) As [NULLIF] Example-2: Declare @FisrtName varchar ( 100 ), @LastName varchar ( 100 ) Set @FisrtName = 'Rakesh' Set @LastName = 'Kalluri' Select NULLIF ( @FisrtName , @LastName ) As [NULLIF]