How do you do this in mysql or rails

Say you have a posts table and a tags table, and both are related by a post_tags table.

so

posts has id/subject/body columns

tags has id/name

post_tags has id/post_id/tag_id

in rails terminology, I have a Post Model that has many Tags through AssetTags.

I'm trying to query for a post that has 2 specific tags. so if there is a rails tag and a mysql tag, I want a query that returns a post that only has those two tags.

make sense?

Any way to do this with activerecord (I'm using search logic) or mysql?

This SQL returns the posts that contain both tags.

select 
  p.* 
from 
  posts p
  ,asset_tags atg1
  ,asset_tags atg2
  ,tags t1
  ,tags t2
where
  p.id = atg1.post_id
and t1.id = atg1.tag_id
and t1.tag = 'MySQL' 
and p.id = atg2.post_id
and t2.id = atg2.tag_id
and t2.tag = 'Rails'
;

As for doing it via Active record, an alternative would be to query for each of the tags and then & the resulting arrays to get the intersection of the two.