Question

I have 3 tables :

Post, PostComment and Comment.

It’s a many-to-many relation.

I want to select for each post the last comment.
So something like (select * from comment order by create_at DESC limit 1) doest not work here.

And I want something like:

select *
  from post as p
    left join post_comment as pc on (pc.post_id = p.id)
    left joint comment as c on (c.id = pc.comment_id)
    left joint comment as c2 on (c2.id = pc.comment_id and c2.id > c.id)
  where c2.id is null

It works very well for one-to-many relation, but I can’t get ride of this for many-to-many.

Note: I renamed my table. In my code, I do not use comment and post. And I do need a many-to-many relation.

Thanks you

Answer 1

I did something like that :

select *
  from post as p
    left join post_comment as pc on (pc.post_id = p.id)
    left join comment as c on (c.id = pc.comment_id)
    left outer join
            (post_comment as pc2
                inner join comment as c2 on (c2.id = pc2.comment_id)
            ) on (bc2.post_id = p.id and c1.created_at < c2.created_at)
  where c2.id is null