mysql - mysql 查询应该是什么来获取一组存储在同一个表中的用户最近添加的消息

Question

我有以下表结构

我希望结果是

这是我尝试过的查询

select * from table where userid IN(201,202,203,204,205)
group by userid
order by messageid desc

但我力求根据 messageid 获取最新记录。我需要在一个查询中写这个，因为我必须使用 order by 子句

请解释我的错误并提供解决方案

Answer 1

SELECT yourtable.*
FROM
  yourtable INNER JOIN (SELECT userid, MAX(messageid) max_messageid
                        FROM yourtable
                        WHERE userid IN (201,202,203,204,205)
                        GROUP BY userid) mx
  ON yourtable.messageid=mx.max_messageid
     AND yourtable.userid=mx.userid

Answer 2

如果我正确理解您的问题，您可以使用max的将表格连接到自身：messageid

select t.messageid, t.userid, t.data
from yourtable t
  join (
    select max(messageid) maxmessageid, userid
    from yourtable
    where userid in (201,202,203,204,205)
    group by userid
    ) t2 on t.userid = t2.userid and t.messageid = t2.maxmessageid
order by t.messageid desc

• SQL 小提琴演示

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编辑：这是使用的替代方法IN：

select messageid, userid, data
from yourtable
where messageid in (
    select max(messageid) maxmessageid
    from yourtable
    where userid in (201,202,203,204,205)
    group by userid
    ) 
order by messageid desc

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