sql左连接给出重复的多个值

Question

我无法获取正确结果的 friend 请建议，在此先感谢。 我有两个表并试图获得平衡数量

一个是采购表(purchase_detail)

Pur_Date    Item_Id     Pur_Qty
2014-10-08  12792       25
2014-11-01  133263      20
2014-10-01  133263      2
2014-11-20  12792       10

其次是销售表(sale_detail)

Sale_Date   Item_Id  Sale_Qty
2014-11-17  133263     -6
2014-11-05  12792      -1
2014-11-24  133263     -2
2014-10-28  12792      -6
2014-11-05  133263     -2

使用左连接后 SQL :

select a.pur_item,  sum(a.pur_qty  + b.sold_qty ) as bal_qty
from purchase_item_qty_amount  a left join  sale_item_qty_amount b 
on a.pur_item =b.sale_item  where a.pur_item IN( 12792,133263)
group by 1;

结果 - 但它不正确

Item_Id   Bal_qty 
12792     56
133263    46

结果 - 应该是

Item_Id    Bal_qty
12792      28
133263     12

Answer 1

试试这个未经测试的查询:

select pur_item, sum(as bal_qty) from (
select pur_item,  sum(a.pur_qty) as bal_qty
from purchase_item_qty_amount  a
group by 1
union 
select pur_item, sum(b.sold_qty)as bal_qty
from sale_item_qty_amount b
group by 1)
group by 1