mysql中JOIN上的重复列名

问题描述

此sql有问题

SELECT COUNT( * )
FROM (

  SELECT *
  FROM `user` `t`
  JOIN `user_relation` r ON ( t.user_id = r.follower_id
  OR t.user_id = r.user_id )
  WHERE r.status = "active"
  AND (
    r.user_id =125
    OR r.follower_id =125
  )
  AND t.user_id !=125
  GROUP BY t.username
)sq

我总是收到错误消息:#1060-重复的列名'user_id'"任何人都可以帮忙/解释一下，我做错了什么吗?

I always get an error: "#1060 - Duplicate column name 'user_id' " Can anyone help/explain, what I did wrong?

先谢谢了扬

推荐答案

您需要在内部查询中提供别名列

You need to provide aliased column in inner query

SELECT COUNT( * )
FROM (

  SELECT t.*
  FROM `user` `t`
  JOIN `user_relation` r ON ( t.user_id = r.follower_id
  OR t.user_id = r.user_id )
  WHERE r.status = "active"
  AND (
    r.user_id =125
    OR r.follower_id =125
  )
  AND t.user_id !=125
  GROUP BY t.username
)sq

由于您只对count(*)感兴趣，因此您只能返回t.*或r.*或任一列，条件是内部查询必须中的列名称必须唯一，或者如果在两个表中都相同，但前缀是表别名.

Since you are interested in count(*) only you can return either t.* or r.* or any one column , the condition being that column names in inner query MUST be unique or if are same in both tables than prefixed with table alias name.

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