如何在MySQL中为每个topic_id选择最后两个记录 [英] How to select the last two records for each topic_id in MySQL
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问题描述
我必须为每个主题选择最后两个记录.
I have to select the last two records for every topic.
例如: 表格:味精
id | topic_id
------------
1 | 1
2 | 1
3 | 1
4 | 1
5 | 2
6 | 2
7 | 2
8 | 3
9 | 3
10 | 3
我想获得这些行:
3 1
4 1
6 2
7 2
9 3
10 3
我该怎么做?
谢谢
推荐答案
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
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