mysql - 来自其他列的值的最大函数问题

Question

我有以下 MySQL 查询：

Select match_static_id, comments as last_comment, max(timestamp)
from comments as c 
group by match_static_id;

我有对比赛的评论表，我想获得每场比赛的最新评论。所以我为此使用 max(timestamp) 和 group by (match_static_id) 但我的问题是我得到了按 match_static_id 分组的最大时间戳，但我得到了其他评论（不是最大时间戳的评论）我的查询是否以错误的方式排序？

Answer 1

这将解决：

SELECT match_static_id, comments AS last_comment, login_time2
  FROM  comments c
WHERE timestamp=
    ( SELECT MAX(timestamp) AS login_time2
      FROM comments WHERE match_static_id=c.match_static_id)
 GROUP BY match_static_id;

Answer 2

我不是mysql专家，但我能感觉到这个问题。可能是因为注释不是 group by 的一部分，它会返回匹配 match_static_id 的所有行。我建议重写如下内容：

select match_static_id, (select Comment from comments c where c.timestamp =max(a.timestamp)) as last_comment, max(timestamp) from comments group by match_staic_id

或者

select c.match_static_id, c.comments as last_comment, c.timestamp from comments c inner join (Select max(timestamp) as ts from comments group by match_static_id) temp c.timestamp = temp.ts