One of the newest features in MySQL, and one of its most eagerly-anticipated ones, is subqueries. Subqueries have been on the MySQL wishlist for a while; they've finally made an appearance in MySQL 4.1, and, as someone who's been playing with them for a little while, I can tell you that they're pretty useful. Sadly, however, since the software is still under development, there isn't too much information available at the moment on their full capabilities in the MySQL context.