php中的更新查询不会更新

Question

当我尝试更新库管理系统中的某些数据时，数据不会更新。它只是保存相同的数据。这是代码：

if(isset($_POST['submit'])){
    $postID         = @$_POST['stud_id'];
    $getID          = @$_GET['stud_id'];
    $postFullName      = $_POST['fullname'];
    $postEmail      = $_POST['email'];
    $postContact      = $_POST['contact'];
    $postSection    =$_POST ['section'];
    $postUsername   = $_POST['username'];
    $postPassword   = $_POST['password'];
    $postType       = $_POST['type'];
    $postStatus     = $_POST['status'];
    $rs3 = $db->query("SELECT * FROM users WHERE stud_id = '$postID' ");
    $check = $rs3->num_rows;

if ($check > 0) 
{
    if ($action == "edit") 
    {
        $edit = $db -> query("UPDATE users SET stud_id='$postID', fullname = '$postFullName', email = '$postEmail' , contact = '$postContact', section = '$postSection',username = '$postUsername',password = '$postPassword',type = '$postType', status = '$postStatus' WHERE user_id = '$postID' ");
        echo "Record Updated.";
    } 
    else 
    {
        $edit = $db -> query("UPDATE users SET stud_id='$postID', fullname = '$postFullName', email = '$postEmail' , contact = '$postContact', section = '$postSection',username = '$postUsername',password = '$postPassword',type = '$postType', status = '$postStatus' WHERE user_id = '$postID' ");
        echo "Record Updated.";
    }
}