$orders = $this->getOrdersFromPackingSlip($packingslip_id);
       $in = str_repeat('?,', count($orders) - 1) . '?';
       $sql = "SELECT
                   o.id as order_id, ps.productid, ps.id as productstock_id, ps.location
               FROM
                   orders AS o
                       INNER JOIN
                   orders_items AS oi ON oi.orderid = o.id
                       INNER JOIN
                   products_stock AS ps ON ps.productid = oi.itemid
                       AND ps.id = oi.productstockid
               WHERE
                   o.id IN ($in)";
       $stmt = $this->db->prepare($sql);
       $stmt->execute($orders);
       $data = $stmt->fetchAll(PDO::FETCH_GROUP);
       foreach ($data as $order_id => $values) {
           foreach ($values as $column) {
               # code...
           }
           # code...
       }