SQL Trees

Hi there

I have a table that holds categories and another table that holds products.

In the category table, i have a parent and parent-child categories, at the moment, a parent can have max. of 2 children.
In the products table i have a foreign key reference any of the categoryID in the category table.

Now I would like do delete a category. If I delete a parent category, then all the products that reference the categoryid are replaced by a permanent misc. categoryid. On the other hand if a child-category is deleted, then the products are shifted one-up to the the parent category of the deleted category.

Could you help me with the delete and maybe updating of the category and products SQL queries.

Thanks in advance!