Probelm with MySQL register.

[Mitch]

could you fix it for me?

You can restrict double values with UNIQUE.
Your problem isn't the database, but how you process the results.
E.g.

		case "register": 
   hasLogin = searchForLogin(username); 
   if (!hasLogin) {
      createAdmin(username, password);
   } 
	

Note: this is not working code that you can just copy and paste and use. Just an example.