Select * From
(
Select a.货物编号 as dataid,sum(b.銷貨數量) as TotalNum,
Sum(b.銷貨數量*b.銷貨价格) From 銷貨頭表 a,銷貨明細表 b where a.id=b.id where a.date>='日期1'
And a.Date<='日期2' Group by b.货物编号
Union All
Select a.货物编号 as dataid,sum(b.銷貨數量) as TotalNum,
Sum(b.退貨頭表*b.退貨明細表) From 銷貨頭表 a,銷貨明細表 b where a.id=b.id where a.date>='日期1'
And a.Date<='日期2' Group by b.货物编号
) a ,產品資料表 b where a.Dataid=b.dataid