Question

我想做的是检索包含两个常见列（电影和年份）的所有人：

login_id | movie               | year
---------|---------------------|-----------
john     | the matrix          | 1999
john     | star wars           | 1977
bob      | titanic             | 1997
johnny   | the matrix          | 1999
tony     | lord of the rings   | 2001
tony     | lord of the rings   | 2002
tony     | lord of the rings   | 2003
james    | star wars           | 1977
robert   | star trek           | 1966
james    | titanic             | 1997
bob      | star trek           | 1966
...

所以，如果我有兴趣找到login_id: bob他看过的电影，还有谁看过同样的电影预期输出：

login_id | movie               | year
---------|---------------------|-----------
james    | titanic             | 1997
robert   | star trek           | 1966
...

我想尽可能有效地做到这一点，如果我需要重组表格，我会这样做。第一个猜测：

SELECT login_id, movie, year, count(*) FROM watchers GROUP BY login_id, movie, year HAVING count(*) > 1 **and login_id = 'bob'**

＆＃39;＆＃39;＆＃39;是我困惑的地方，因为它是按计数分组而不是拉出所有常见数据。

Answer 1

我在想exists：

select w.*
from watchers w
where exists (select 1
              from watchers w2
              where w2.movie = w.movie and w2.year = w.year and w2.login_id = 'bob'
             );

Answer 2

我建议使用自我加入：

Select t1.*
From  table t0
Join table t1 on t0.movie = t1.movie
And t0.year = t1.year
Where t0.login_id ='bob'

使用SQL查询进行树搜索以查找公共单元

2 个答案: