mySQL query for selecting children

Question

I am not sure if this is possible in mySQL. Here are my tables:-

Categories table:

• id
• name
• parent_id (which points to Categories.id)<

Answer 1

Bear with me, because I have never done something like this.

BEGIN
  SET cat = "5";
  SET temp = "";

  WHILE STRCMP(temp, cat) != 0 DO
    SET temp = cat;
    SET cat = SELECT CONCAT_WS(GROUP_CONCAT(id), cat) FROM Categories GROUP BY (parent_id) HAVING FIND_IN_SET(parent_id, cat);
  END LOOP;
END;

SELECT * FROM products WHERE FIND_IN_SET(category_id, cat)

I can almost guarantee the above won't work, but you can see what I'm trying to do. I got this far and I just decided to not finish the end of the query (select the top N from each category), sorry. :P