中级mySQL查询 - 将两个表连接在一起并限制结果

Question

Here is my table arrangement:

Posts
   post_id
   post_votes

Comments
   comment_id
   post_id
   comment_time

I have failed to create a query that does the following:

1. Select 10 Posts Order By post_votes desc
2. While getting 5 comments for each post

I will post what I have tried if necessary. I am just getting into more complicated queries, any help or suggestions is greatly appreciated

Answer 1

The below will retrieve 10 post order by desc and also 5 comments order by desc respectively.

select post_id,post_votes,comment_id,comment_time,
 @rn := CASE WHEN @prev_post_id = post_id THEN @rn + 1 ELSE 1 END AS rn,
        @prev_post_id := post_id from
  (select p.post_id,post_votes,comment_id,comment_time from
  (SELECT post_id,post_votes from posts order by post_votes desc limit 10) p 
   left outer join 
   comments c on p.post_id=c.post_id order by post_id,comment_time desc )m
having rn<=5

SQL FIDDLE HERE (testing sample of retrieving 3 post order by desc and also 2 comments for each post respectively).