mysql - 如何使用Max聚合函数获取行的值？

Question

我有一个评论表:

+----------+---------------------+----------+
| match_id |     timestampe      | comment  |
+----------+---------------------+----------+
|      100 | 2014-01-01 01:00:00 | Hi       |
|      200 | 2014-01-01 01:10:00 | Hi1      |
|      300 | 2014-01-01 01:20:00 | Hi2      |
|      100 | 2014-01-01 01:01:00 | Hello    |
|      100 | 2014-01-01 01:02:00 | Hello1   |
|      200 | 2014-01-01 01:11:00 | hey      |
+----------+---------------------+----------+

我想从表格中获取以下信息

SELECT match_id, max(timestampe) as maxtimestamp, count(match_id) as comments_no
FROM comments
GROUP BY match_id
order by maxtimestamp DESC

前面的解释效果很好，但问题是当我想获取 maxtimestamp 的注释时。

如何使用最优化的查询获取每场比赛的最新评论(最大时间戳的评论)？

Answer 1

你可以这样做。 这也是相当理想的。

SELECT c.comment, m.* 
FROM 
comments c 
JOIN
(
    SELECT t.match_id, max(t.timestampe) as maxtimestamp, count(t.match_id) as comments_no
    FROM comments t
    GROUP BY t.match_id
) m on c.match_id = m.match_id and c.timestampe = m.maxtimestamp

SQL Fiddle