sql - MySQL中如何为每个topic_id选择最后两条记录

Question

我必须为每个主题选择最后两条记录。

例如:表:消息

id  |  topic_id
------------
 1  |  1
 2  |  1
 3  |  1
 4  |  1
 5  |  2
 6  |  2
 7  |  2
 8  |  3
 9  |  3
10  |  3

我想获取这些行:

 3 1
 4 1
 6 2
 7 2
 9 3
10 3

我该怎么做？

Answer 1

SELECT max(id), max(topic_id) FROM msg
GROUP BY topic_id

UNION

SELECT max(id), max(topic_id) FROM msg
WHERE id not in (
    SELECT max(id) as id FROM msg
    GROUP BY topic_id)
GROUP BY topic_id