Searching on categories.

I have a database like this. PRODUCTS id product cat_id 1 keyboard 3 2 mouse 3 3 windows 2 4 PowerPC 4 Then I also have another database like this. CATEGORIES id name parent_id 1 PC 0 2 Software 1 3 Hardware 1 4 Mac 0 So categories can have a parent of 0 or another category. Products have one category. I can perfectly search for a product in 1 category. I am having some problems with the recursion involved in searching the subcategories of a category. I can search like this. SELECT * FROM PRODUCTS WHERE cat_id='2' The result would be "3 windows 2". But what if I want to search the whole cat_id 1? (so it will include cat 2 and cat 3)? Please some one point me. -Roman. My other computer is spongy gray matter.