MySQL COUNT（）多列 [英] MySQL COUNT() multiple columns

问题描述

我正在尝试从数据库中的所有视频中提取最热门的标签（忽略空白标签）。我也需要'flv'为每个标签。我有这个工作，因为我想如果每个视频有一个标签：

I'm trying to fetch the most popular tags from all videos in my database (ignoring blank tags). I also need the 'flv' for each tag. I have this working as I want if each video has one tag:

SELECT tag_1, flv, COUNT(tag_1) AS tagcount 
  FROM videos 
 WHERE NOT tag_1='' 
 GROUP BY tag_1 
 ORDER BY tagcount DESC LIMIT 0, 10

但是，在我的数据库中，每个视频都有三个标签 - tag_1，tag_2和tag_3。

However in my database, each video is allowed three tags - tag_1, tag_2 and tag_3. Is there a way to get the most popular tags reading from multiple columns?

记录结构是：

+-----------------+--------------+------+-----+---------+----------------+ 
| Field           | Type         | Null | Key | Default | Extra          | 
+-----------------+--------------+------+-----+---------+----------------+ 
| id              | int(11)      | NO   | PRI | NULL    | auto_increment | 
| flv             | varchar(150) | YES  |     | NULL    |                | 
| tag_1           | varchar(75)  | YES  |     | NULL    |                | 
| tag_2           | varchar(75)  | YES  |     | NULL    |                | 
| tag_3           | varchar(75)  | YES  |     | NULL    |                | 
+-----------------+--------------+------+-----+---------+----------------+ 

推荐答案

您需要取消转移数据：

SELECT tag, COUNT(*)
FROM (
    SELECT tag_1 AS tag
    UNION ALL
    SELECT tag_2 AS tag
    UNION ALL
    SELECT tag_3 AS tag
) AS X (tag)
GROUP BY tag
ORDER BY COUNT(*) DESC

$ b b

我不知道如何确定flv是为一个特定的标签，因为每个id可以有一个单一的flv和最多3个标签，似乎任何标签可以有许多不同的flv。

I'm not sure how the flv is determined for a particular tag, since each id can have a single flv and up to 3 tags, it seems like any tag can have many different flv.

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