比较两个表之间的值

Question

我有两个表， Table_A 和 Table_B 。

我想要下面的结果结果，有人可以帮我解决SQL查询吗？

表-A

------------------
ID  ITEM_ID   QTY
------------------
1   100        2
2   101        3
3   102        5
4   103        2
------------------

表-B

------------------
ID  ITEM_ID   QTY
1   100        2
2   101        4
3   102        4
4   104        2
5   105        1
------------------

RESULT

------------------
ITEM_ID   QTY
100        0
101        1
102        -1
103        -2
104        2
105        1
------------------

感谢。

Answer 1

您需要完整联接才能从任一表中获取值

 select
      isnull(a.item_id,b.item_id) as item_id, isnull(b.qty, 0) - isnull(a.qty, 0) as qty
    from
      table_a a
      full outer join table_b b on a.item_id = b.item_id

Answer 2

select item_id, sum(qty)
  from (select item_id, qty
          from table_b
        union all
        select item_id, -qty
          from table_a) x
 group by item_id
 order by item_id

Answer 3

使用完全外连接和一些isnulls

SQL Fiddle Example

select isnull(b.item_id, a.item_id) as ItemID,
  isnull(b.qty, 0) - isnull(a.qty,0)as Qty
from table_b b
full outer join table_a a on a.item_id = b.item_id
order by itemid