Question

我有一个问题：

SELECT b.user_id, b.active FROM users b
WHERE b.followers_count != (SELECT COUNT(*) 
    FROM (SELECT u.user_id
        FROM user_follow uf,users u,user_follow_request ufr
        WHERE
        uf.following_id = b.user_id AND
        uf.following_id = ufr.friend_id AND
        ufr.status = 'approved' AND
        ufr.user_id = u.user_id AND u.user_id != b.user_id AND u.active != 0
        GROUP BY u.user_id) a) 
 AND b.active = -1 limit 5;

必须从user_id中选择与sql计算的列中users不同的所有followers_count。

但问题是我收到错误消息

Error Code: 1054. Unknown column 'b.user_id' in 'on clause'

我做错了什么？非常感谢您的帮助。

Answer 1

您的意思是uf.user_id = b.user_id而不是uf.following_id = b.user_id吗？无论如何，user_follow表用于什么？

同意草莓，你最好使用显式连接。它们更容易阅读和理解。以下是您可能提到的内容（请注意，user_follow表根本没有使用过）：

SELECT u.user_id, u.followers_count, IF(ISNULL(uafc.actual_fc),0,uafc.actual_fc) AS afc
  FROM users AS u
    LEFT JOIN (
      SELECT u.user_id AS user_id, COUNT(*) AS actual_fc
        FROM users AS u
          JOIN user_follow_request AS ufr
            ON ufr.friend_id = u.user_id
          JOIN users AS fu
            ON fu.user_id = ufr.user_id
        WHERE ufr.user_id != u.user_id
          AND ufr.status = 'approved'
          AND fu.active != 0
        GROUP BY u.user_id, u.followers_count
      ) AS uafc
      ON uafc.user_id = u.user_id
  WHERE u.followers_count != IF(ISNULL(uafc.actual_fc),0,uafc.actual_fc)
;

对于NULL解决方法可能有一些更好的解决方案。

在SQLFiddle上查看：http://sqlfiddle.com/#!2/71f6c/3

具有多个子查询的select中的上表可见性

1 个答案: