I need to implement some database tables to track an invitation system.

New customers on this website can register only when a friend invites him. There are two ways of new customers register, with the Email of an existing customer(friend) or with the Card Number of the existing customer(friend).

Here is an image representing this:


Now the MySQL tables... This tables are valid? The PK is the ID of the existing customer and the ID of the new customer. Please see the image of the tables.


Best Regards, André.