嵌套子查询不能与主查询相关

Question

问题

在子查询中的users.user_id中，它是未知的 并且它在主查询中的定义与它们之间没有关系

任务是：

找到user2朋友+与user1相互计数

mysql找到user2好友并与user1获得mutual_count（与每个user2好友）

表用户

user_id |   username
------------------
1       |   user1
2       |   user2
3       |   user3
4       |   user4
5       |   user5

表朋友

user_one_id |   user_two_id
------------------------
1           |   2
1           |   4
2           |   3
2           |   4
3           |   1
5           |   2

预期输出//（user2朋友：使用user1检查结果user_id以获得相互计数）

user_id | mutual_count
------------------------
1       |   2             // user1 and user1 mutual users(user2,user3,user4)
3       |   1             // user3 and user1 mutual users(user2)
4       |   1             // user4 and user1 mutual users(user2)
5       |   0             // user5 and user1 -> No mutual users

mysql语句

SELECT  users.user_id,

(SELECT count(a.friendID) FROM
    (   SELECT user_two_id friendID FROM friends  WHERE user_one_id = users.user_id
        UNION 
        SELECT user_one_id friendID FROM friends WHERE user_two_id = users.user_id
    ) AS a 
    JOIN  
    (   SELECT user_two_id friendID FROM friends WHERE user_one_id = 1
        UNION 
        SELECT user_one_id friendID FROM friends WHERE user_two_id = 1
    ) AS b 
    ON  a.friendID = b.friendID
) as mutual_count
FROM friends LEFT JOIN  users    
ON friends.user_one_id = users.user_id or  friends.user_two_id = users.user_id  
WHERE (friends.user_one_id = 2 OR friends.user_two_id = 2)   AND users.user_id != 2

我得到的错误 未知栏＆＃39; users.user_id＆＃39;在＆＃39; where子句＆＃39; 获取mutual_count canot的问题子查询知道users.user_id

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