php - 'users.user_id' 中的未知列 'where clause'

Question

此语句显示用户 2 的 friend 列表并获取用户 1 的共同 friend 数量。当我运行此语句时，出现以下错误，

:Unknown column 'users.user_id' in 'where clause'

查询

 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

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

Answer 1

内部查询

 SELECT user_one_id friendID FROM friends WHERE user_two_id = users.user_id

不知道users.user_id是什么