How to prevent duplicate Usernames in php/mysql

Question

(This is my first try with php)

I have a very basic register page. http://graves-incorporated.com/test_sites/member_test/register/register.php

* I j

Answer 1

You can use ajax query before submit to check/prevent is already exists Also in back-end after you do INSERT INTO... you can do SELECT FOUND_ROWS() to check if it's actually equals 1, it means one row inserted. Then redirect user to error page with information what is not correct. For better user experience, I recommend first option, with JQuery it will not take a lot of time to implement.