สอบถามการแก้ไข update เมื่อกดแล้วไม่ขึ้นเออเร่อขึ้นแต่หน้าว่างเปล่าค่ะ

<?php
     ini_set('display_errors', 1);
     error_reporting(~0);
  
     $serverName = "localhost";
     $userName = "sa";
     $userPassword = "";
     $dbName = "nomneaw";
  
     $striduser = null;
  
     if(isset($_GET["id"]))
     {
       $striduser = $_GET["id"];
     }
    

	$serverName = "localhost";
	$userName = "root";
	$userPassword = "";
	$dbName = "nomneaw";

	$Con = mysqli_connect($serverName,$userName,$userPassword,$dbName);

    $SQL = "SELECT * FROM register WHERE id = '".$striduser."' ";
    $Query = mysqli_query($Con,$SQL);
	$Result = mysqli_fetch_array($Query,MYSQLI_ASSOC);
?>
  
  
<div class="container">
  <div class="row">
    <div class="col-xs-12 col-sm-12 col-md-12">
    <h3>Edit Staff</h3>
    <p> <hr>
    <div class="col-xs-12 col-sm-12 col-md-12">
    <input type="hidden" name="id" id="id"  value="<?php echo $Result['id'];?>" />
    <div class="box-body">
          <div class="row">
            <div class="col-md-6">
              <div class="form-group">
               <label>Firstname</label>
               <input type="text" class="form-control" id="firstname" name="firstname" value="<?php echo $Result['firstname'];?>">
               
               </div>
            </div>
            <div class="col-md-6">
              <div class="form-group">
               <label>Lastname</label>
               <input type="text" class="form-control" id="lastname" name="lastname" value="<?php echo $Result['lastname'];?>">
               </div>      
            </div>
        </div>
        <div class="row">
            <div class="col-md-4">
              <div class="form-group">
               <label>Username</label>
               <input type="text" id="username" name="username" class="form-control" value="<?php echo $Result['username'];?>">
               </div>
            </div>
            <div class="col-md-4">
              <div class="form-group">
               <label>Password</label>
               <input type="password" id="password" name="password" class="form-control"value="<?php echo $Result['password'];?>" >
               </div>      
            </div>
            <div class="col-md-4">
              <div class="form-group">
               <label>Confirm Password</label>
               <input type="password" id="repassword" name="repassword" class="form-control"value="<?php echo $Result['repassword'];?>">               
               </div>
            </div>
        </div>
        <div class="row">
            <div class="col-md-6">
              <div class="form-group">
               <label>Telephone</label>
               <input type="text" id="tel" maxlength="10" name="tel" class="form-control" value="<?php echo $Result['tel'];?>" >
               </div>
            </div>
            <div class="col-md-6">
              <div class="form-group">
               <label>Status</label>
               <input type="text" id="status" maxlength="10" name="status" class="form-control" value="<?php echo $Result['status'];?>" readonly="readonly" >
               </div>      
            </div>
        </div>
        
        <a href="admin_page.php"><button type="button" class="btn btn-danger pull-left" >Undo</button></a>

        <button type="submit" name="Submit" class="btn btn-warning pull-right button_save" >Save</button>
        </div>
    </div>
  </div>
</div>

<?php
	ini_set('display_errors', 1);
	error_reporting(~0);

	$serverName = "localhost";
	$userName = "root";
	$userPassword = "";
	$dbName = "nomneaw";

	$conn = mysqli_connect($serverName,$userName,$userPassword,$dbName);

	$sql = "UPDATE register SET 
			firstname = '".$_POST["firstname"]."',
			lastname = '".$_POST["lastname"]."',
			username = '".$_POST["username"]."',
			`password` = '".$_POST["password"]."',
			repassword = '".$_POST["repassword"]."',
			tel = '".$_POST["tel"]."',
			`status` = '".$_POST["status"]."'
			WHERE id = '".$_POST["id"]."' ";

	$query = mysqli_query($conn,$sql);
    
	if($query) {

	    $message = "Update successful!";
        echo "<script type='text/javascript'>alert('$message');</script>";
        echo "<script>window.location='admin_page.php'</script>";
	}

	mysqli_close($conn);
?>