php - MySQL一对多关系，具有共享值

Question

我有一个包含 3 个表的 MySQL 数据库。

简介， p_tags, 标签

数据库:

profile
pid | name

ptags
ptid | pid | tagid

tags
tagid | tag

数据库看起来像这样

profile
pid | name
 1    Randy
 2    Jeff
 3    Mike

ptags
ptid | pid | tagid
 1      1      1
 2      1      2 
 3      2      1
 4      2      3 
 5      3      1
 6      3      2
 7      3      3 

tags
tagid | tag
  1     science
  2     filosophy
  3     hydrology

我需要创建一个查询，显示配置文件中具有共享标签的名称和共享标签总数

即.

Results
Name  | Name2 | Count
Randy - Jeff - 1
Randy - Mike - 2
Jeff - Randy - 1
Jeff - Mike - 2 
Mike - Randy - 2
Mike - Jeff - 2

等等。

不知道我解释的对不对。

我读了

https://www.simple-talk.com/sql/t-sql-programming/divided-we-stand-the-sql-of-relational-division/

来自另一个与此类似的帖子的链接，但我无法理解它:)。

SQLFiddle:http://sqlfiddle.com/#!9/42bde6

Answer 1

在查询中使用连接:

SELECT p1.name Name1, p2.name Name2, Count(tagid)
FROM ptags AS t1
INNER JOIN ptags AS t2 ON t2.tagid = t1.tagid and t2.ptid <> t1.ptid 
INNER JOIN profile AS p1 ON p1.pid = t1.pid 
INNER JOIN profile AS p2 ON p2.pid = t2.pid 
GROUP BY p1.name, p2.name

如果一对名字只需要一行，那么试试这个:

SELECT p1.firstname Name1, p2.firstname Name2, Count(t1.tagid)
FROM profile_hashtags AS t1
INNER JOIN profile_hashtags AS t2 
  ON t2.tagid = t1.tagid and t2.pHid > t1.pHid 
INNER JOIN `profile` AS p1 ON p1.pid = t1.pid 
INNER JOIN `profile` AS p2 ON p2.pid = t2.pid 
GROUP BY p1.firstname, p2.firstname;