Question

您好我尝试按照几个例子来解决我的问题，但没有成功。

所以这是情况

我有一张包含以下内容的表格（每个月都会增加表格）

mysql> DESCRIBE poraba;
+------------+------------+------+-----+-------------------+-----------------------------+
| Field      | Type       | Null | Key | Default           | Extra                       |
+------------+------------+------+-----+-------------------+-----------------------------+
| mesec      | timestamp  | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| voda_mrzla | varchar(5) | NO   |     | NULL              |                             |
| voda_topla | varchar(5) | NO   |     | NULL              |                             |
+------------+------------+------+-----+-------------------+-----------------------------+

使用以下vaules

mysql> SELECT * FROM poraba;
+---------------------+------------+------------+-----------+
| mesec               | voda_mrzla | voda_topla | id_poraba |
+---------------------+------------+------------+-----------+
| 2014-03-03 16:19:08 | 5985       | 3417       |         1 |
| 2014-04-03 20:57:51 | 5978       | 3412       |         2 |

我想执行以下操作。始终只在最后一次进入。所以我得到了当前和上个月之间的差异。

例如：

voda_mrzla (from 2014-04-03) - voda_mrzla (from 2014-03-03) = difference_cold
voda_topla (from 2014-04-03) - voda_topla (from 2014-03-03) = difference_hot

进入

mysql> DESCRIBE usage_per_month;
+-----------------+-------------+------+-----+---------+-------+
| Field           | Type        | Null | Key | Default | Extra |
+-----------------+-------------+------+-----+---------+-------+
| difference_cold | varchar(10) | NO   |     | NULL    |       |
| difference_hot  | varchar(10) | NO   |     | NULL    |       |

Answer 1

看起来糟糕的数据库设计。您至少应该有一个带有增量值的id列作为键。这样（但仍然很繁琐）查询会更容易一些。鉴于您目前的设计，您需要做的是（非常，非常慢和低效）：

insert into usage_per_month
select a.voda_mrzla - b.voda_mrzla, a.voda_topla - voda_topla
from ( select * from poraba where mesec = ( select max(mesec) from poraba) ) as a,
( select * from poraba where mesec = ( select max(mesec) from poraba where mesec <> (select max(mesec) from poraba) ) ) as b;

是的，这很难看。

Answer 2

将所有“varchar”更改为“int”将ID添加到所有表并执行以下操作解决了我的问题

INSERT INTO usage_per_month (difference_cold, difference_hot) 
SELECT p1.voda_mrzla - p2.voda_mrzla AS poraba_mrzla1, p1.voda_topla - p2.voda_topla AS poraba_topla1 FROM poraba p1
  LEFT JOIN poraba p2 ON p2.`id_poraba` = (
    SELECT MAX(`id_poraba`) FROM poraba p3 WHERE p3.`id_poraba` < p1.`id_poraba`
  ) ORDER BY p1.id_poraba DESC LIMIT 1

Tnx寻求帮助！

减去最后两行并将结果写入新表MySQL

2 个答案: