選擇與限制

Question

這裏獨特的是一個例子：

正如你可以看到，前4條記錄有相同數量的topic_id。我如何獲得唯一topic_id的最後10條記錄？

謝謝。

PS正確的結果，例如：

id  user_id topic_id ... 
306114 14331  26164  ... 
306110 14331  27001  ... 
306109 14331  26660  ... 
...  ...  ...  ... 

Answer 1

SELECT posts.id, posts.user_id, posts.text, posts.topic_id, posts.updated_at, topics.name as topic_name, topics.forum_id FROM my_forum_posts AS posts 
         ... 
         WHERE posts.id IN (SELECT MAX(id) FROM my_forum_posts GROUP BY topic_id) 
         ORDER BY posts.id DESC LIMIT 10