MySQL Cannot Add Foreign Key Constraint

Question

So I\'m trying to add Foreign Key constraints to my database as a project requirement and it worked the first time or two on different tables, but I have two tables on which

Answer 1

I got the same error. The cause in my case was:

1. I created a backup of a database via phpmyadmin by copying the whole database.
2. I created a new db with the same name the old db had und selected it.
3. I started an SQL script to create updated tables and data.
4. I got the error. Also when I disabled foreign_key_checks. Altough the database was completely empty.

The cause was: Since i used phpmyadmin to create some foreign keys in the renamed database - the foreign keys where created with a database name prefix but the database name prefix was not updated. So there were still references in the backup-db pointing to the newly created db.