PHP表单更新不会更新

Question

我已经编写了表单的编辑部分但不知道它不会更新已编辑的字段。该代码不会给出任何错误，但它不会更新？！

如果有可能，有人可以看一下吗？

<?php
include "connect.php";//database connection

if (isset($_GET["id"])) {
  $id = intval($_GET["id"]);

  if (isset($_POST["edited"])) 
  {
    $update  = "UPDATE traumprojekt SET";
    $update .= sprintf("quantityProduct='%s', " , mysql_real_escape_string($_POST["quantityProduct"]));
    $update .= sprintf("titleProduct='%s', " , mysql_real_escape_string($_POST["titleProduct"]));
    $update .= sprintf("informationProduct='%s'", mysql_real_escape_string($_POST["informationProduct"]));
    $update .= "WHERE id = '$id'";
    mysql_query($update);
  }

  $sql = "SELECT * FROM `traumprojekt` WHERE id=$id";

  $res = mysql_query($sql) or die (mysql_error());

  if (mysql_num_rows($res) == 1) 
  {
    $row = mysql_fetch_assoc($res);


?>

<form method="post" action="edit_form.php?id=<?php echo $row["id"] ?>">
  ID: <?php echo $row["id"] ?><br />
  Quantity: <input type="text" name="quantityProduct" value="<?php echo $row["quantityProduct"] ?>"><br />
  Product Title: <input type="text" name="titleProduct" value="<?php echo $row["titleProduct"] ?>"><br />
  Product Information: <input type="text" name="informationProduct" value="<?php echo $row["informationProduct"] ?>"><br />
  <input type="submit" name="submit" value="Update"><br />
  <input type="hidden" name="edited" value="1">
</form>

<?php

  }

}

?>