得到每個答案10條評論通過一個查詢

Question

我有一個意見表，就像這樣：
id，answer_id，content

現在我想每個答案ID最新10條評論。
答案ID列表提供像（1,5,11,27,82）

是否有可能通過一個查詢獲得所有相關評論？

我目前做到這一點通過PHP的的foreach：

foreach ($answers as $answer) { // query mysql for its comments 

Answer 1

可以使用UNION ALL每個answer_id：

(select id, answer_id, content from comments where answer_id=1 order by id desc limit 10) 
union all 
(select id, answer_id, content from comments where answer_id=5 order by id desc limit 10) 
union all 
(select id, answer_id, content from comments where answer_id=11 order by id desc limit 10) 
union all 
(select id, answer_id, content from comments where answer_id=27 order by id desc limit 10) 
union all 
(select id, answer_id, content from comments where answer_id=82 order by id desc limit 10); 

Answer 2

SELECT * FROM comments LIMIT 10; 

的LIMIT只會返回指定的沒有結果的。它會返回結果

Answer 3

的第n個這是MySQL中的痛苦，但你可以使用變量：

select c.* 
from (select c.*, 
      (@rn := if(@a = c.answer_id, @rn + 1, 
         if(@a := c.answer_id, 1, 1) 
         ) 
      ) as rn 
     from comments c cross join 
      (select @rn := 0, @a := -1) params 
     order by answer_id, id desc 
    ) c 
where rn <= 10; 

這假定較大的id值更近一些。