保存表行的新位置jquery ui sortable，MySQL

i want to allows users to sort table rows derived from database and save the new location in database the problem is that the postion is not updated in the interface nither in the database mysql table: id int primary key auto_increment, sort int, author_affliation varchar, author_email varchar

script:

$('#myTable tbody').sortable({
                    start: function (event, ui) {
                        //fix firefox position issue when dragging.
                        if (navigator.userAgent.toLowerCase().match(/firefox/) && ui.helper !== undefined) {
                            ui.helper.css('position', 'absolute').css('margin-top', $(window).scrollTop());
                            //wire up event that changes the margin whenever the window scrolls.
                            $(window).bind('scroll.sortableplaylist', function () {
                                ui.helper.css('position', 'absolute').css('margin-top', $(window).scrollTop());
                            });
                        }
                    },
                    beforeStop: function (event, ui) {
                        //undo the firefox fix.
                        if (navigator.userAgent.toLowerCase().match(/firefox/) && ui.offset !== undefined) {
                            $(window).unbind('scroll.sortableplaylist');
                            ui.helper.css('margin-top', 0);
                        }
                    },
                    helper: function (e, ui) {
                        ui.children().each(function () {
                            $(this).width($(this).width());
                        });
                        return ui;
                    },
                    scroll: true,
                    update: function (event, ui) {
                        serial = $(this).sortable('serialize');
                        $.ajax({
                            url: "sort_coauthors.php",
                            type: "POST",
                            data: serial,
                            success: function(response) {
                              alert(response);
                            },
                            error: function(){
                                alert("theres an error with AJAX");
                            }
                        });
                    }
                }).disableSelection();

sort-coauthors:

@mysql_connect("localhost", "root", "") or die(mysql_error());
mysql_select_db("mydb") or die(mysql_error());

if (isset($_POST['menu']) && is_array( $_POST['menu'])) {
$menu = $_POST['menu'];
for ($i = 0; $i < count($menu); $i++) {
    $q = mysql_query("UPDATE `co_authors` SET `sort`=" . $i . " WHERE `id`='" . intval($menu[$i]) . "'") or die(mysql_error());
if($q) {
    echo "success";
}
}
}
else {
    echo "fail";
}

main page:

while ($row = mysql_fetch_assoc($co_authors)) {

                    echo "<tbody><tr id='menu_" . $row['id'] . "'><td>{$row['author_email']}</td>
                     <td>{$row['coauthor_affliation']}</td>";
                    ?><td><button class='remove' id='remove' name='remove' email="<?php echo $row['author_email'] ?>"
                            paper="<?php echo $row['paper_id'] ?>">Remove</button></td>