Query to find posts with an exact set of tags (many-to-many relationship)

Question

Suppose I have the following three tables expressing a relationship where posts are given tags (a many-to-many relationship):

create table posts (id integer, con         


        

Answer 1

Should be able to do this use NOT EXISTS, e.g.,

select t1.post_id
from post_tags as t1
    inner join post_tags as t2 on t2.post_id = t1.post_id
where 
    t1.tag = 'clever' 
and t2.tag = 'interesting' 
and not exists (
    select *
    from post_tags t3
    where 
        t3.tag not in ('clever', 'interesting')
    and t3.post_id = t1.post_id
)