How to delete an infinite category and delete all subcategories under it at the same time_PHP Tutorial

$act = isset ($_GET['act']) ? trim ($_GET['act ']) : ";
if ($act == 'del')
{
$sort_id = isset ($_GET['id']) ? intval($_GET['id']) : '0' ;
$sort_ids = $sort_id;
$childrenIds = getChildrenIds ($sort_id);
if (!empty ($childrenIds))
{
$sort_ids .= $ childrenIds;
}
$sql = "delete from `article_sort` WHERE `sort_id` in ({$sort_ids})";
$res = mysql_query ($sql);
if ($res )
{
alert ('Deletion successful');
exit;
}
else
{
alert ('Deletion failed');
exit;
}
}

/*—— —————————————————— */
//– Get the subcategory ID set under the infinite category ID
//– $sort_id = $sort_id.getChildrenIds($sort_id );
//– $sql = " ….. where sort_id in ($sort_id)";
/*—————————————————————— */
function getChildrenIds ($sort_id)
{
global $db;
$ids = ";
$sql = "SELECT * FROM ".$db->table('article_sort') ." WHERE `parent_id` = '{$sort_id}'";
$res = $db->query ($sql);
if ($res)
{
while ($ row = $db->fetch_assoc ($res))
{
$ids .= ','.$row['sort_id'];
$ids .= getChildrenIds ($row['sort_id ']);
}
}
return $ids;
}