Mysql 检查两个用户是否喜欢彼此的项目

我有三张桌子：

用户

+----+------+
| id | name |
+----+------+
|  1 | Foo  |
|  2 | Bar  |
|  3 | La   |
+----+------+

+----+-------+
| id | owner |
+----+-------+
|  1 |     2 |
|  2 |     1 |
|  3 |     2 |
+----+-------+

+----+------+---------+---------+
| id | vote | user_id | item_id |
+----+------+---------+---------+
|  1 |    1 |       1 |       1 |
|  2 |    1 |       2 |       2 |
|  3 |   -1 |       3 |       1 |
|  4 |    1 |       1 |       2 |
|  5 |   -1 |       3 |       2 |
+----+------+---------+---------+

项目

+----+------+
| id | name |
+----+------+
|  1 | Foo  |
|  2 | Bar  |
|  3 | La   |
+----+------+

+----+-------+
| id | owner |
+----+-------+
|  1 |     2 |
|  2 |     1 |
|  3 |     2 |
+----+-------+

+----+------+---------+---------+
| id | vote | user_id | item_id |
+----+------+---------+---------+
|  1 |    1 |       1 |       1 |
|  2 |    1 |       2 |       2 |
|  3 |   -1 |       3 |       1 |
|  4 |    1 |       1 |       2 |
|  5 |   -1 |       3 |       2 |
+----+------+---------+---------+

投票

+----+------+
| id | name |
+----+------+
|  1 | Foo  |
|  2 | Bar  |
|  3 | La   |
+----+------+

+----+-------+
| id | owner |
+----+-------+
|  1 |     2 |
|  2 |     1 |
|  3 |     2 |
+----+-------+

+----+------+---------+---------+
| id | vote | user_id | item_id |
+----+------+---------+---------+
|  1 |    1 |       1 |       1 |
|  2 |    1 |       2 |       2 |
|  3 |   -1 |       3 |       1 |
|  4 |    1 |       1 |       2 |
|  5 |   -1 |       3 |       2 |
+----+------+---------+---------+

现在，我想写一个查询，检查两个特定的用户ID是否彼此相似

我希望获得两个匹配项的ID

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编写此查询最有效的方法是什么？我已经创建了一个SQLFIDLE:

我首先要做一个简单的连接，以获得一个用户列表和他们喜欢的用户

SELECT user_id AS id1, items.owner AS id2 FROM votes
       JOIN items ON items.id=item_id;

这将给出一个带有2个ID的表。然后将此表与其自身连接，并检查每个表是否相等。所以

SELECT * FROM temp t1 JOIN temp t2
    WHERE t1.id1=t2.id2 AND t1.id2=t2.id1

将这两个要素组合在一起，您将得到：

SELECT * FROM
  (SELECT user_id AS id1, items.owner AS id2 FROM votes
JOIN items ON items.id=item_id) table1
JOIN
  (SELECT user_id AS id1, items.owner AS id2 FROM votes
JOIN items ON items.id=item_id) table2
WHERE
  table1.id1=table2.id2 AND table1.id2=table2.id1;

您不清楚您想要的是哪种输出，但这将输出一个包含两列的表，其中每个人都有一个相互类似的列表

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但是，可能有一个更有效的方法不涉及子查询。

您想要布尔值（num行）或recods of like？您是否确实尝试过自己编写查询？请告诉我们你已经做出了什么努力。