mysql 减法联合问题

Question

例如:我有 4 个表: 表1:项目

item_id    name   quantity
==========================
1          a      10
2          b      15

表 2:附加

add_id     name   quantity  item_id
===================================
1          c      5         1

表 3:item_out(这将减去项目数量)

item_id    quantity
==========================
1          10
2          5

表 4:additional_out(这将减去额外数量)

additional_id     quantity
==========================
1                 5         

我的问题是:我应该给出什么mysql查询才能得到这些结果？

item_ id   quantity   additional_id    additinal_quantity
=================================================
1          5          1                0
2          15

因为我使用mysql查询代码如下:

SELECT item_id, SUM(quantity - IFNULL(number,0)), additional_id, SUM(additional_quantity - IFNULL(additional_number,0))
FROM(
   SELECT a.item_id, a.quantity, b.additional_id, b.quantity AS additional_quantity, NULL AS number, NULL AS additional_number
   FROM table_1 a JOIN table_2 b ON some condition
   UNION
   SELECT NULL AS item_id , NULL AS quantity,... a.quantity AS number, b.quantity AS additional_number
   FROM table_3 a JOIN table_4 b ON condition
)AS T

由于第一个选择中的 SUM，它仅以 1 行结束。

Answer 1

试试这个:

SELECT item_ id, 
  (item.quantity - IFNULL(item_out.quantity,0)) AS quantity, 
  additional_id, 
  (IFNULL(a.quantity,0) - IFNULL(ao.quantity,0)) AS additional_quantity
FROM item
LEFT JOIN item_out
ON item.item_id = item_out.item_id
LEFT JOIN additional a
ON item.item_id = a.item_id
LEFT JOIN additional_out ao
ON a.addid = ao.additional_id