Question

我有一个评论表，如下所示：
id，answer_id，content

现在我想获得每个答案ID的最新10条评论答案ID列表如（1,5,11,27,82）

是否可以通过一个查询获取所有相关评论？

我目前通过php的foreach：

执行此操作

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

Answer 1

这是MySQL的痛苦，但您可以使用变量：

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;

这假设较大的id值更新。

Answer 2

您可以为每个answer_id使用UNION ALL：

(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 3

SELECT * FROM comments LIMIT 10;

LIMIT将仅返回指定的结果数。它将返回前n个结果

通过一个查询获得每个答案的10条评论

3 个答案: