Question

I have two tables – forum_topics and topics_posts. I want to select rows from forum_topics which have no posts in the topics_posts table, but cannot figure out how to. Does an SQL statement like this exist:

select from * `forum_topics` where have no rows in `topics_posts`

Answer 1

I think you want something like that:

select * from forum_topics t
where not exists (
    select * from topics_posts p
    where p.topic_id = t.id
);

Although using an outer join, might be a bit faster than the subquery:

select * from forum_topics t left outer join forum_posts p
on t.id = p.topic_id
where p.id is null;