问MySQL不会从PHP更新-我的代码可能出了什么问题？

EN

$rf = $_GET['_id'];
//$_GET['_id']; is generated by ME

if ( ! empty($rf))
{
$mysqli->query("UPDATE cse SET clicks = clicks + 1 WHERE code='" . $rf ."'");
}
//this works. it adds 1 to the counter of clicks column for that referring users row


if($_POST['email']){

    // Requested with AJAX:
    $ajax = ($_SERVER['HTTP_X_REQUESTED_WITH']  == 'XMLHttpRequest');

    try{
        if(!filter_input(INPUT_POST,'email',FILTER_VALIDATE_EMAIL)){
            throw new Exception('Invalid Email!');
        }

        $mysqli->query("INSERT INTO cse
                        SET email='".$mysqli->real_escape_string($_POST['email'])."'");

        if($mysqli->affected_rows != 1){
            throw new Exception('exists in the database.');
        } else {   
          $ecode = add_code($mysqli->insert_id); 
        } 
        if(!empty($rf)){
          $mysqli->query("UPDATE cse SET sign_ups = sign_ups + 1 WHERE code='" . $rf ."'");
//this does not work. it should add 1 to the counter of sign_ups column for that referring users row
        }

        if($ajax){
            die(json_encode(array('msg' => $msg)));
        }

    }
    catch (Exception $e){

        if($ajax){
            die(json_encode(array('error'=>$e->getMessage())));
        }

        $msg = $e->getMessage();        
    }
}

$.post("./index.php",{email:$('#email').val()},function(r){

            if(r.error){
                $('#email').val(r.error);
                        } else {
                $('#email').val(r.msg);
            }           
            working = false;
        },'json');