trying to DELETE a row with PHP and MYSQL

Solution:

You called the parameter item and not id.

$id =  $_GET['id'];

should hence be

$id =  $_GET['item'];

Solution:

You probably need to check if the get isset if(isset($_GET['item'])) { var_dump($_GET['item']); }

Solution:

In your attribute tag you are using item as query string .

<a href="mark.php?as=done&item=<?php echo $item['id']; ?>

But you are getting data with wrong query string id. You should use below one.

if($_GET['delete']){

   $id =  $_GET['item'];