gistfile1.php

        $sql = "SELECT ID FROM ".$wp_prefix."users WHERE user_login = '".$member_info['username']."'";
          $result = mysql_query($sql,$con);
            $num_rows = mysql_num_rows($result);
              mysql_close($con);
        if($num_rows > 0) {
                echo "NOTOK";
                exit;
        } else {
                echo "OK";
                exit;
        }