SQL(sum of two collumns located in different tables store procedure)

--PRECEDURE NAME--

Create Procedure spRawMaterialUseageReport

--DECLARE VARIABLE FOR ID--

@ID as int=0

As

--DECLARE VARIABLES--

Declare @ExtraQua as int

Declare @MenuQua as int

IF NOT Exists (Select TableNameONE.Quantity From TableNameONE Where TableNameONE.RawMaterialID = @ID)

BEGIN

SET @ExtraQua = 0

END

ELSE

BEGIN

Select @ExtraQua = Sum(MenuExtrasRawMaterials.Quantity) From MenuExtrasRawMaterials Where MenuExtrasRawMaterials.RawMaterialID = @ID

END

--/////////////////////////////////////////--

IF NOT Exists (Select TableNameTWO.Quantity From TableNameTWO Where TableNameTWO.RawMaterialID = @ID)

BEGIN

SET @MenuQua = 0

END

ELSE

BEGIN

Select @MenuQua = Sum(TableNameTWO.Quantity) From TableNameTWO Where TableNameTWO.RawMaterialID = @ID

END

IF NOT (@ID) = 0

BEGIN

Select TableNameTHREE.ID , TableNameTHREE.Name , (@ExtraQua + @MenuQua) As QuantityUsed, TableNameTHREE.UoM From TableNameTHREE Where TableNameTHREE.ID = @ID

END

GO