Question

我正在使用MySQL，我有两张桌子。一个具有对值的引用，另一个具有实际值。我想计算SUM。

ItemMess

+----+--------+----------+---------------------+
| ID | ItemID | MessType | TimeStamp           |
+----+--------+----------+---------------------+
| 1  | 2      | 1        | 2015-04-26 18:53:33 |
+----+--------+----------+---------------------+
| 2  | 2      | 2        | 2015-04-26 18:54:42 |
+----+--------+----------+---------------------+
| 3  | 2      | 1        | 2015-04-26 18:54:49 |
+----+--------+----------+---------------------+
| 4  | 2      | 1        | 2015-04-26 18:55:01 |
+----+--------+----------+---------------------+
| 5  | 2      | 2        | 2015-04-26 18:55:04 |
+----+--------+----------+---------------------+

MessTypes

+------------+--------------+---------------+
| MessTypeID | MessTypeName | MessTypeValue |
+------------+--------------+---------------+
| 1          | Mess Up      | 1             |
+------------+--------------+---------------+
| 2          | Mess Down    | -1            |
+------------+--------------+---------------+

因此，如果您看到，MessTypeID引用了MessTypes表中的值。我想要sum和up的{{1}}。所以，如果我进行如下查询：

down

我得到了这个输出：

SELECT *, (
  SELECT `MessTypeValue` FROM `MessTypes` WHERE `MessTypeID`=`MessType`
) AS `Val` FROM `ItemMess` GROUP BY `ItemID`

但如果我给出：

+----+--------+----------+---------------------+
| ID | ItemID | MessType | TimeStamp           |
+----+--------+----------+---------------------+
| 1  | 2      | 1        | 2015-04-26 18:53:33 |
+----+--------+----------+---------------------+
| 2  | 2      | 2        | 2015-04-26 18:54:42 |
+----+--------+----------+---------------------+
| 3  | 2      | 1        | 2015-04-26 18:54:49 |
+----+--------+----------+---------------------+
| 4  | 2      | 1        | 2015-04-26 18:55:01 |
+----+--------+----------+---------------------+
| 5  | 2      | 2        | 2015-04-26 18:55:04 |
+----+--------+----------+---------------------+

或者

SELECT *, (
  SELECT `MessTypeValue` FROM `MessTypes` WHERE `MessTypeID`=`MessType`
) AS `Val`, SUM(SELECT `MessTypeValue` FROM `Messtypes` WHERE `MessTypeID`=`MessType`) AS `Mess`FROM `ItemMess` GROUP BY `ItemID`

我收到以下错误：

查询错误（1064）：第1行'SELECT SELECT *, ( SELECT `MessTypeValue` FROM `MessTypes` WHERE `MessTypeID`=`MessType` ) AS `Val`, SUM(`Val`) AS `Mess`FROM `ItemMess` GROUP BY `ItemID` FROM MessTypeValue WHERE messtypes = MessTypeID）FROM''附近的语法错误

和

查询错误（1054）：“字段列表”中的未知列'Val'

我该如何处理。我想要MessType的值。有没有办法，我可以用SUM替换原始值中的1和2？ ps：我不想为整个事物创建一个视图或使用IDs。

Answer 1

使用联接：

select im.ItemID, sum(mt.MessTypeValue) as val
from ItemMess im
join MessTypes mt on im.MessTypeID = mt.MessTypeID
group by im.ItemID

没有加入：

select  im.ItemID, (select sum(mt.MessTypeValue) from MessTypes mt where im.MessTypeID = mt.MessTypeID) as val
from ItemMess im
group by im.ItemID

Answer 2

我错过了什么或者你正在寻找这个吗？

select i.id, sum(messtypevalue) 
  from itemmess i
    inner join messtypes t
      on i.messtype = t.messtypeid
  group by i.itemid;

demo

这会产生以下输出：

ID  |  sum(messtypevalue)
 1  |   1

Answer 3

这应该适合你：

SELECT `i`.`id`,
       Sum(`messtypevalue`)
FROM   `itemmess` AS `i`
       INNER JOIN `messtypes` AS `t`
               ON `i`.`messtype` = `t`.`messtypeid`
GROUP  BY `i`.`itemid`;

SUM中的子查询

3 个答案: