如何通过多个元组(行)找到共享一个属性(列)的对？

Question

我试图在这个简化的例子中找到喜欢同一组电视节目的用户对

假设我有一张桌子,每个用户都可以获得他们喜欢的每个电视节目的参赛作品:

|USER | Show        |
|-----|-------------|
|001  | Lost        |
|001  | South Park  |
|002  | Lost        |
|003  | Lost        |
|003  | South Park  |
|004  | South Park  |
|005  | Lost        |
|006  | Lost        |

然后我想得到一个结果:

|USER1 |USER2 |
|------|------|
|001   |003   |
|003   |001   |
|002   |005   |
|002   |006   |
|005   |002   |
|005   |006   |
|006   |002   |
|006   |005   |

或者更好的版本是:

|USER1 |USER2 |
|------|------|
|001   |003   |
|002   |005   |
|002   |006   |
|005   |006   |

基本上说:用户1喜欢与用户3相同的节目集.

我一直在玩GROUP BY和JOIN,但我仍然找不到答案:(.

到目前为止,我发现使用了

SELECT s1.User as USER1, s2.User as USER2, s1.Show as Show 
FROM Shows s1 JOIN (SELECT * FROM Shows) s2 
ON s1.Shows=s2.Shows AND s1.User!=s2.User;

这产生了成对的用户和他们共同的展示.但我不知道从哪里开始.

Answer 1

如果您可以接受 CSV 而不是表格结果，则只需将表格分组两次即可：

SELECT GROUP_CONCAT(User) FROM (
  SELECT   User, GROUP_CONCAT(DISTINCT `Show` ORDER BY `Show` SEPARATOR 0x1e) AS s
  FROM     Shows
  GROUP BY User
) t GROUP BY s

否则，您可以将上面的子查询连接到其自身：

SELECT DISTINCT LEAST(t.User, u.User) AS User1,
             GREATEST(t.User, u.User) AS User2
FROM (
  SELECT   User, GROUP_CONCAT(DISTINCT `Show` ORDER BY `Show` SEPARATOR 0x1e) AS s
  FROM     Shows
  GROUP BY User
) t JOIN (
  SELECT   User, GROUP_CONCAT(DISTINCT `Show` ORDER BY `Show` SEPARATOR 0x1e) AS s
  FROM     Shows
  GROUP BY User
) u USING (s)
WHERE t.User <> u.User

在sqlfiddle上查看它们。

当然，如果保证表中不存在重复(User, Show)对，您可以通过从聚合中删除关键字来提高性能。ShowsDISTINCTGROUP_CONCAT()