Mysql 聚合函数与查询中的某列冲突

我有两张桌子：

users:
 ___________________________
|user_id        | username  |
|_______________|___________|
|  1            |  Dolly    |
|  2            |  Didi     |
|_______________|___________|

forum:
 _____________________________________________________________
|match_static_id| comment   | timpstamp            | user_id  |
|_______________|___________|______________________|__________|
|  1            |  Hi       | 2013-07-10 12:15:03  |     2    |
|  1            |  Hello    | 2013-07-09 12:14:44  |     1    | 
|_______________|___________|______________________|__________|

SELECT  forum.match_static_id,
count(forum.match_static_id) 'comments_no', max(forum.timestamp)'timestamp', users.username
FROM forum
INNER JOIN users on users.id = forum.user_id
GROUP BY forum.match_static_id

此查询工作正常，仅使用thw

论坛

表：

SELECT  forum.match_static_id,
count(forum.match_static_id) 'comments_no', max(forum.timestamp)'timestamp'
FROM forum
GROUP BY forum.match_static_id
Order BY timestamp DESC

但以下查询使用两个表：

users:
 ___________________________
|user_id        | username  |
|_______________|___________|
|  1            |  Dolly    |
|  2            |  Didi     |
|_______________|___________|

forum:
 _____________________________________________________________
|match_static_id| comment   | timpstamp            | user_id  |
|_______________|___________|______________________|__________|
|  1            |  Hi       | 2013-07-10 12:15:03  |     2    |
|  1            |  Hello    | 2013-07-09 12:14:44  |     1    | 
|_______________|___________|______________________|__________|

SELECT  forum.match_static_id,
count(forum.match_static_id) 'comments_no', max(forum.timestamp)'timestamp', users.username
FROM forum
INNER JOIN users on users.id = forum.user_id
GROUP BY forum.match_static_id

在这里，我想得到max（timestamp）的用户，但我得到了错误的用户。任何人都能给我一个关于这个的线索吗？ 按时间戳顺序描述尝试以下操作：

SELECT  f1.match_static_id,
  f2.comments_no, 
  f2.maxtimestamp, 
  users.username
FROM forum AS f1
INNER JOIN
(
  SELECT match_static_id, 
    max(timestamp) maxtimestamp,
    count(comment) AS comments_no
  FROM Forum
  GROUP BY match_static_id
) AS f2  ON f1.match_static_id = f2.match_static_id
        AND f1.timestamp = f2.maxtimestamp
INNER JOIN users on users.user_id = f1.user_id;

请在此处查看它的实际操作：

---

您想要

max（时间戳）

foreach

匹配\u static\u id

还是什么？关于

users.username

您希望为每个分组的

match\u static\u id

选择哪个用户名？我希望注释的用户名为max（时间戳）。这是一个常见问题解答，但如果您看到演示，comment\u no字段给出的是1，它应该是2。我需要max timestamp的用户，但我也需要注释\u noaffected@BaselShbeb-啊哈，好的，对不起，请看我的编辑。从内部查询中选择它。