Aggrigate function SUM return NULL manage by isnull, CALESCE.

Aggrigate function SUM return NULL manage by isnull, CALESCE.

select SUM(fileno) as filedata, SUM(addno) as addre from formA1 where userid=2

 

select SUM(isnull(fileno,0)) as filedata, SUM(isnull(addno,0)) as addre from  (SELECT NULL AS fileno,NULL as addno) formA1

SELECT SUM(fileno) FROM (SELECT  COALESCE(NULL,0)AS fileno)formA1   

OUTPUT: