Two column as a primary keys in mysql?

Question

Today I found out you can have a primary key using two columns (tsql). The PK must be unique but both columns do not (the combo must be unique).

I thought that was v

Answer 1

Yes, this is a normal thing to do in SQL and it works (having a composite primary key, in which multiple fields together constitute a unique value).

Two notes:

1. Make sure it's necessary. It often is and then it's fine. But sometimes it's a sign that you further need to normalize your data model.

2. I'm thinking that you don't want to make and a b be foreign keys from another table and then make them the composite primary key of your table. What happens if you set up a cascading delete, in which one user id, but not the other is deleted? So the composite primary key is fine, but then you don't want come from "unrelated" foreign keys.