Question

我有一个表，我需要按两个不同的列对条目进行分组

这是我的代码

SELECT *
    FROM (
        SELECT max(user_msg.id) AS mid, max(user_msg.timestamp) AS tsp, user_msg.text, 
        usr1.id AS u1_id, usr1.nickname AS u1_nickname, usr1.avatar AS u1_avatar, usr1.avatar_art AS u1_avatar_art, 
        usr2.id AS u2_id, usr2.nickname AS u2_nickname, usr2.avatar AS u2_avatar, usr2.avatar_art AS u2_avatar_art,
        COUNT(user_msg.id) AS cnt
        FROM user_msg 
        join user using (client_id)
        LEFT JOIN user AS usr1 ON user_msg.from_id=usr1.id
        LEFT JOIN user AS usr2 ON user_msg.to_id=usr2.id
        WHERE user_msg.to_id = '".$user_id."' AND to_delete='0' OR user_msg.from_id = '".$user_id."' AND to_delete='0'
        group by u1_id, u2_id ORDER by tsp DESC
    ) c

它应该像u1_id和u2_id

这样的组

请帮助

Answer 1

您需要使用原始列名称，而不是别名。它们尚未处理（好吧，在SQL Server中它们不是：不确定MYSQL）。

...
   WHERE user_msg.to_id = '".$user_id."' AND to_delete='0' OR user_msg.from_id = '".$user_id."' AND to_delete='0'
  group by usr1.id, usr2.id
  ORDER by tsp DESC
...

修改：MySQL allows aliases in the GROUP BY

所以，我怀疑GROUP BY是错误的和模棱两可的，需要像下面的标准SQL一样。有或没有别名

喜欢这个问题：SQL Query not showing expected result

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注意，要制作此标准SQL（或在任何其他RDBMS上运行），您需要使用GROUP BY中不在聚合中的所有列：

    SELECT
       max(user_msg.id) AS mid, 
       max(user_msg.timestamp) AS tsp, 
       user_msg.text, 
       usr1.id AS u1_id, usr1.nickname AS u1_nickname, usr1.avatar AS u1_avatar, usr1.avatar_art AS u1_avatar_art, 
       usr2.id AS u2_id, usr2.nickname AS u2_nickname, usr2.avatar AS u2_avatar, usr2.avatar_art AS u2_avatar_art,
       COUNT(user_msg.id) AS cnt
    FROM user_msg 
    join user using (client_id)
    LEFT JOIN user AS usr1 ON user_msg.from_id=usr1.id
    LEFT JOIN user AS usr2 ON user_msg.to_id=usr2.id
    WHERE user_msg.to_id = '".$user_id."' AND to_delete='0' OR user_msg.from_id = '".$user_id."' AND to_delete='0'
    GROUP BY 
          user_msg.text, usr1.id, usr1.nickname, usr1.avatar, usr2.avatar_art,
          usr2.id, usr2.nickname, usr2.avatar, usr1.avatar_art
    ORDER by tsp DESC

SQL GROUP BY多列

1 个答案: