Question

I have a DB structured like this:

CATEGORIES > SUBCATEGORIES > PRODUCTS

In just want show the categories which have an number of products related to it, but I don’t know if my method is the best.
I thinking in putting some SELECT statement inside the first WHERE, but this sounds “unpratical”.
I searched into Google/MySQl docs and nothing helped me.

Example of what I have done with CATEGORIES > SUBCATEGORIES:

SELECT c.*
FROM categories c
WHERE 
(
   SELECT count(*)
   FROM subcategories sc
   WHERE sc.id_categories = c.id
) > 2

With this query I can sucessfully see which categories have more than 2 subcategories related to them, I just could do the same, adding the PRODUCTS table to this query. But I almost sure this is going to slow the query. There is some more fast way of doing this type of query?
Thanks!

Answer 1

Something like this, I don’t know your FK relations, so I’m just guessing here.

SELECT *
FROM Categories
WHERE EXISTS(
  SELECT NULL
  FROM products
  JOIN SubCategories ON products.fkSubCatID = SubCategories.PkSubCatID
  WHERE SubCategories.fkCatID = Categories.pkCatID
  HAVING Count(*) > 2)