I'm looking for a registration without "username"
You just put your email there twice and your password.
the php explodes the email to username @ blablabla.com
saves de 'username' on the table and the password.
saves the email normal
users should login with or without @blablabla.com
if occurs, makes de sistem input a new field, to type the username and the email, normal.
everyone who does not have the same email before @ logins really fast.
doesnt matter if u can or cannot chage your username or email, because tables are the same that actually are