Mysql get the common categories of products

Question

I am trying to create a filtering sistem for products.

I have:

• products table
• categories table: id, id_parent, name
• associations table: id_category, id_product

I want to search the table of products and from the results to create the common categories that they have so they can be filtered even more.

How do I get only the categories that are found in all the products list?

Thanks for any help!

Answer 1

You can use the following query:

SELECT id_category
FROM (SELECT id_category, COUNT(DISTINCT id_product) AS cnt
      FROM associations
      GROUP BY id_category ) AS t
WHERE t.cnt = (SELECT COUNT(DISTINCT id) FROM products)

This will return all category ids that are related to all products stored in the products table.

Demo here