我有下表，其中parent_id、价格、数量和exp_date是主要字段。
+-----------+-------+----------+------------+---------------------+------------------+
| parent_id | price | quantity | exp_date | last_modified | last_modified_by |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 410 | 3.00 | 2016-07-30 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 300 | 10.00 | 0000-00-00 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 540 | 17.00 | 2016-07-22 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
我想从最后修改的行开始的总量中减去一个不同的值。 现在我有这个查询:
SET @remain = -19;
Update Stock_props SET quantity =
(SELECT IF((@remain := quantity+@remain) < 0,'0',@remain) as quantity)
WHERE parent_id = 2
ORDER BY last_modified DESC
这个特定的值正在工作，因为我减去的值大于最后一行。它将输出:
+-----------+-------+----------+------------+---------------------+------------------+
| parent_id | price | quantity | exp_date | last_modified | last_modified_by |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 410 | 0.00 | 2016-07-30 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 300 | 0.00 | 0000-00-00 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 540 | 11.00 | 2016-07-22 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
但是，如果我想减去较小的数量(例如 11)，结果将如下所示:
+-----------+-------+----------+------------+---------------------+------------------+
| parent_id | price | quantity | exp_date | last_modified | last_modified_by |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 410 | 2.00 | 2016-07-30 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 300 | 0.00 | 0000-00-00 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 540 | 19.00 | 2016-07-22 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
而不是这个:
+-----------+-------+----------+------------+---------------------+------------------+
| parent_id | price | quantity | exp_date | last_modified | last_modified_by |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 410 | 0.00 | 2016-07-30 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 300 | 2.00 | 0000-00-00 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
| 2 | 540 | 17.00 | 2016-07-22 | 2016-07-22 18:14:34 | test |
+-----------+-------+----------+------------+---------------------+------------------+
我在这里缺少什么？ 预先感谢您!
最佳答案
好吧，如果将来有人偶然发现这个问题，以下查询可以完美地工作:
ALTER TABLE Stock_props ADD helper numeric;
SET @remain = 11;
Update Stock_props SET quantity =
(SELECT IF(((@remain := quantity+@remain) < 0),0,@remain) as quantity),
helper = (SELECT IF((@remain>0), @remain:=0,@remain)as helper),
ORDER BY last_modified DESC;
ALTER TABLE Stock_props DROP helper;
上面的工作原理如下:
- 向名为 helper 的表添加一个新行
- 设置数量和@remain的值(后者是必要的，因为如果它是负数，我们要继续减法)
- 根据符号覆盖@remain的值
- 删除辅助行
关于php - MySQL 在一个查询中从多行中减去，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38450274/