如何编写具有两个左连接和两个计数的 MySql 查询

Question

I have three tables posts,comments,likes and I want to fetch all posts with their amount of likes and comments I've tried this

SELECT posts.id,COUNT(comments.postId) as num_of_comments,COUNT(likes.postId) as num_of_likes                                                                     
FROM posts
LEFT JOIN comments ON comments.postId = posts.id
LEFT JOIN likes ON likes.postId = posts.id
GROUP BY posts.id

Answer 1

You should use the left join for on the subquery with group by result

select  posts.id, t1.num_of_comments, t2.num_of_likes
from posts
leftjoin (
  select comments.postId, COUNT(*) as num_of_comments
  from comments 
  group by comments.postId
) t1 on t1.postId = posts.id
leftjoin (
  select likes.postId, COUNT(*) as num_of_likes
  from likes
  group by likes.postId
) t2 on t2.postId = posts.id