Problem with sessions when registering PHP?

Question

PHP

Wrote a website from scratch. I start sessions in an include with connection of a database.
Wrote registration, did everything as it should, everything works.
When you register the first account, log in - everything is fine.
But when you register a second account, you log in through the second one, then on the site all the information is displayed from the first account, but actions with the database occur with the second account. That is, if you change the email in the settings on the site, then it changes for the second account in the database.

Answer 1

Understood. Forgot about WHERE.