How to bind session to user id?

Question

PHP

Hello. I am writing a simple online store for a term paper. There are several databases, including a database of users with their id, login, etc. The entire basket is stored in $_SESSION['basket']. And the login and id of the already authenticated user is stored in $_SESSION['user']. Sessions have a +1 week lifetime and are stored in the site folder.
Problem actually with division of sessions of each user. If one user logs out and another logs in on the same computer, the same basket opens. How to tell Sessions to open an old session whose name, for example, begins with the user id?
The teacher will not check the code, the main thing is that it works.

Answer 1

If the user is authorized, then store his cart in the database. Otherwise - in session.