کدش شبیه اینه
createFunction [dbo].[udf_SumPrice](

@idenID bigint

)

returns bigint 

as

begin

    Declare @Sum bigint

    select @Sum =SUM(Price) from "tblName"            where idenID =@idenID  

                                   tblName.idenID =@idenID  

                    if @Sum is null

                        set  @Sum =0

                    

                    return @Sum 

end

حالا این select روبنویس
select dbo.SumPrice from "tblname"