带有 SUM() 的 MySQL 查询未返回预期结果 [英] MySQL query with SUM() is not returning the expected results

问题描述

查询:

SELECT 
    id_data,
    id_tag IN (75) AS tag1,
    id_tag IN (12) AS tag2,
    SUM(id_tag IN (75, 12)) summedTags
FROM
    tags_inservice
WHERE id_service = 1 
GROUP BY id_data 
ORDER BY summedTags DESC

结果:

id_data    tag1    tag2  summedTags
-------  ------  ------  ----------
   3109       0       1           2
   1956       0       0           2
   1928       0       0           1
   2738       1       0           1

我认为不对的地方:

summedTags 很少与标签的实际总和相匹配！在示例中，id_data 3109 有 0 + 1 = 2，这是错误的，而 id_data 1956 显示 0 + 0 = 2，这也是错误的，等等.我做错了什么?

The summedTags rarely matches the actual sum of the tags! In the example id_data 3109 has 0 + 1 = 2 which is wrong, and id_data 1956 shows 0 + 0 = 2 which is wrong too, etc, etc. What am I doing wrong?

顺便说一句，我也尝试添加 HAVING SUM(id_tag IN (75, 12)) = 2 ，结果相似.

By the way, I also tried adding HAVING SUM(id_tag IN (75, 12)) = 2 with similar results.

如果您需要更多额外信息:

我有一个表 tags_inservice 包含一堆数据(由 id_data 表示，来自另一个表的 id)并且数据可以用不同的标签进行标记.一个 id_data 可以有零个或多个 id_tags，因此可能会有不止一行具有相同的 id_data 值.事实上，有时用相同的 id_tag 多次标记相同的 id_data 是有效的.

I have a table tags_inservice that contains a bunch of data (represented by id_data, an id from another table) and the data can be tagged by different tags. An id_data can have zero or more id_tags so there could be more than one row with the same id_data value. In fact, sometimes it's valid to have the same id_data tagged with the same id_tag more than once.

DESCRIBE tags_inservice;

Field       Type     Null    Key     Default  Extra         
----------  -------  ------  ------  -------  --------------
id_intag    int(11)  NO      PRI     (NULL)   auto_increment
id_tag      int(11)  YES     MUL     (NULL)                 
id_service  int(11)  YES     MUL     (NULL)                 
data_type   int(11)  YES             (NULL)                 
id_data     int(11)  YES     MUL     (NULL)                 

推荐答案

似乎问题是由 group by 引起的，因为 summedTags 是 id_data

seems the problem is caused by group by as the summedTags is the occurrences of id_data

SELECT 
id_data,
sum(if (id_tag=75,1,0)) as tag1,
sum(if (id_tag=12,1,0)) as tag2,
sum(if (id_tag in(12,75),1,0)) as summedTags
FROM tags_inservice
WHERE id_service = 1 
GROUP BY id_data 
ORDER BY summedTags DESC;

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