无法在 max 函数上聚合 [英] Can't aggregate on max function

问题描述

我有一张桌子

CREATE TABLE `messages` ( `uid` BIGINT NOT NULL ,
`mid` BIGINT , `date` BIGINT NOT NULL  , PRIMARY KEY (`mid`));

我想选择按 uid 分组的 max(date)，即对于每个 uid(read user)，我想找到最新消息(具有最大日期)

I want to select max(date) grouped by uid, i.e. for every uid(read user) I want to find the latest message (with tha maximum date)

试过了

select messages.mid,  max(messages.date), messages.uid, messages.body 
                                   from messages 
                             where messages.chat_id is  NULL 
                                   group by messages.uid 

但是查询出错了.

推荐答案

子查询可以为您提供所需的日期，以便为每个用户检索最新消息:

A subquery can give you the date you need in order to retrieve the newest message for each user:

SELECT messages.uid, messages.mid, messages.date, messages.body
FROM messages
WHERE messages.chat_id IS NULL
AND messages.date IN 
( SELECT MAX(m2.date) FROM messages m2 
  WHERE m2.uid = messages.uid AND m2.chat_id IS NULL 
)
;

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