deleting a site leaves tables in database

I deleted a site, but the tables in the database still exist. That is, the wp_2_posts, etc tables do not get deleted when the site gets deleted. Then if a add another site, wp_3_posts, etc get created but the wp_2_ stuff is still there taking up space. And there is no easy way to delete them via mySQL … there is do wildcard in DROP TABLES. I think that when you delete a site, everything should get deleted.