Question

In my MySQL products table there is a column called groups which products can belong to. What is actually stored in this column are id’s of another tabled called groups.

What if I want to select products that belong to a specific group?

If a product can only belong to a single group, I could simply use

where group={groupid}

But what if a product can belong to multiple groups?

I could store them like this: ‘4,8,10,42‘, each of these numbers meaning a group id.
But then how would I query a select?

Answer 1

You should not store a list of products in a single field. Instead of a column products.groups, you should have a separate table product_groups (product_id, group_id), where you store each association between a product and a group. Then you can select all products from a group as this:

SELECT product.*
FROM product_groups
INNER JOIN products ON (products.id = product_groups.product_id)
WHERE product_groups.group_id = :group_id`