MySQL 与库存维护

Question

我有一个简单的程序来管理某些车辆的燃油发放状态

即包括下表

商店商品

+---------+-----------+--------+
| item_id | item_name | status |
+---------+-----------+--------+
|       1 | Diesel    |      1 |
+---------+-----------+--------+

tbl_车辆

+------------+------------+
| vehicle_id | vehicle_no |
+------------+------------+
|          1 |       4545 |
|          2 |       4546 |
|          3 |       4547 |
|         18 |       4548 |
+------------+------------+

store_update_stock

+-----------------+------------+---------+--------+
| update_stock_id | bill_date  | bill_no | status |
+-----------------+------------+---------+--------+
|               1 | 2019-09-25 |     123 |      1 |
|               2 | 2019-09-26 |     456 |      1 |
+-----------------+------------+---------+--------+

store_update_stock_details

+-------------------------+-----------------+------+-----+--------+
| update_stock_details_id | update_stock_id | item | qty | status |
+-------------------------+-----------------+------+-----+--------+
|                       1 |               1 |    1 | 900 |      1 |
|                       2 |               2 |    1 | 800 |      1 |
+-------------------------+-----------------+------+-----+--------+

tbl_fuel

+---------+------------+-------------+------+----------+
| fuel_id | vehicle_id | issued_date | item | fuel_qty |
+---------+------------+-------------+------+----------+
|       1 |          2 | 2019-09-25  |    1 |       50 |
|       2 |          2 | 2019-09-25  |    1 |       50 |
|       3 |         18 | 2019-09-26  |    1 |       25 |
|       4 |          2 | 2019-09-27  |    1 |       50 |
+---------+------------+-------------+------+----------+

我使用了以下代码

select sum(store_update_stock_details.qty) - tbl_fuel.fuel_qty  as qty
            from store_update_stock_details
            inner join store_update_stock on store_update_stock_details.update_stock_id=store_update_stock.update_stock_id
           join store_item on store_update_stock_details.item=store_item.item_id
            join tbl_fuel on store_item.item_id=tbl_fuel.item
           where store_update_stock.status=1
           group by store_item.item_id

期望出局

+------+
| qty  |
+------+
| 1525 |
+------+

但是代码生成以下输出

+------+
| qty  |
+------+
| 6750 |
+------+

我不明白可能出了什么问题。谁能帮我吗？

Answer 1

查询的主要问题是，由于 tbl_fuel 中有多个行与库存更新详细信息表中的相同 item 匹配，因此最终会得到多个正在求和的结果集中的行(因此结果大于预期结果)。要解决此问题，您需要分别对每个表中的项目进行求和，然后减去结果:

select susd.qty - tf.fuel_qty  as qty
from (select susd.item, sum(susd.qty) AS qty
      from store_update_stock_details susd
      join store_update_stock sus on sus.update_stock_id = susd.update_stock_id
      where sus.status = 1
      group by item) susd
join store_item si on susd.item = si.item_id
join (select item, sum(fuel_qty) AS fuel_qty
      from tbl_fuel
      group by item) tf on si.item_id=tf.item

输出:

qty
1525

Demo on dbfiddle