How to insert addition of two data field value in third data field value

MY TABLE IS LIKE THAT

ID int identity(1,1),

A int,

B int

SUM int,

I HAVE CREATED WEB PAGE FROM THAT PAGE IM ADDING TWO VALUE

@a

@b

insert into table(A,B,SUM) value(@a,@b,(@a+@b))

but not working any other method for this in sql server

Sms