i know that we already had a lot of question about this error, but i can not fix my code, so anyone here please help me fix this problem. my code like this
function login($username, $password) {
    $user_id = user_id_from_username($username);
    $username = sanitize ($username);
    $password = md5 ($password);
    return (mysql_result(mysql_query("SELECT COUNT (`user_id`) FROM `users` 
        WHERE `username` = '$username' AND `password` = '$password'"),0)==1) ? $user_id : false;
i am looking forward to hear from you guys. i am a new member on this so please keep your answer as simple as possible. thank you.
 
     
     
     
     
    