PHP - Help Outputting Xml From Php $_post In A Loop And Preg_split

Hi, I'm having issues trying to add up the totals of each product type in a while loop- I'm sure it's straightforward to fix but for some reason I can't find a way to get it to add up all the totals of the various product types and list them so we have say 5 of product 1, 11 of product 2, 8 of product 3 and so on.

So firstly the user searches between two different dates / times to get the orders made during that time period: (I'm using separare date and time fields as the datetime-local input doesn't work in a lot of browsers)

if($_POST['search'])
{
    $searchdate1 = mysqli_real_escape_string($conn, $_POST['_Date1']);
    $searchdate2 = mysqli_real_escape_string($conn, $_POST['_Date2']);
    
    $searchtime1 = mysqli_real_escape_string($conn, $_POST['_Time1']);
    $searchtime2 = mysqli_real_escape_string($conn, $_POST['_Time2']);
    
    $datetime1 = $searchdate1 . ' ' . $searchtime1;
    $datetime2 = $searchdate2 . ' ' . $searchtime2;
    
    $nicedate1 = date("l F j, Y", strtotime($searchdate1) ); //Just used for readability in the report
    $nicedate2 = date("l F j, Y", strtotime($searchdate2) );

//Now get the orders from the db

$getorders = $oc_conn->query("SELECT * FROM oc_order WHERE date_added >= '$datetime1' AND date_added <= '$datetime2' AND order_status_id != 0 ORDER BY order_id DESC");

//Then generate start of a table in HTML, the while loop that follows will populate the rows

while ($row = $getorders->fetch_assoc()) { //Get the order data

          $firstname = $row["firstname"];
          $lastname = $row["lastname"];
          $fullname = $firstname . ' ' . $lastname;
        $orderid = $row["order_id"];
        $orderdate = $row["date_added"];    
          $email = $row["email"];
        $total = $row['total'];
          $total = number_format($total, 2);
            
        $niceorderdate = date('F j, Y H:i', strtotime($orderdate));    
            
             echo '<tr><td>'.$fullname.'</td><td>'. $orderid . '</td><td>';
    
            $getproducts = $oc_conn->query('SELECT * FROM oc_order_product WHERE order_id = '.$orderid); //Product names and details are held in a separate table
        
                while ($row = $getproducts->fetch_assoc()) {
                    
                    $orderproductid = $row["order_product_id"];
                    $productname = $row["name"];            
                    $quantity = $row["quantity"];
                    echo $quantity . ' x '.$productname.' <br>'; //This works for each individual order, but what I need is the total $quantity of each $productname, across ALL orders in the time range
                
                }
            echo '</td><td>'. $niceorderdate.'</td></tr>';           
        }
    echo '</tbody></table>';
}
?>

[/PHP]

As mentioned in the comment above, what I need is the total $quantity of each $productname, across ALL orders in the time range, so that I can see how many of each product ($productname) were ordered in total.

I tried using SUM for quantity in the mySQL, and COUNT for adding up the different product names but for some reason it didn't work. Can someone let me know what I need to do? Thanks :)

class coreCartFunctions {

protected function DisplayMenuItems($menu_item_id_session){
	  $qty_output =  "<span style=\"font-size:18px\">X{$this->item_qty}</span>";
      $this->menu_item_name = $this->getItems($this->menu_item_id,"menu_item_name");

           if($this->DisplayPrice()){


             $update_order_url ="item-detail.php?update_order=true&menu_item_id={$menu_item_id_session}
             &callback_url={$this->url}&store={$_SESSION['store_name']}";

             $output =  "<a class='{$this->menu_items_class_prop_a}' href='{$update_order_url}'>
             <div class='{$this->menu_items_class}'>{$qty_output} {$this->menu_item_name}</div>";
             $output .= "<div class='menu_item_price'>\${$this->menu_item_price}</div></a>";
             return $output;
             } else {
             $output = "<a class='{$this->menu_items_class_prop_a}' href='#'><div class='menu_item_name'>"
              .$qty_output." ".$this->menu_item_name ."</div></a>";
             return  $output;
          }



}


class displayCartItems extends coreCartFunctions {

public function GetMenuItems() {

foreach ($this->items as $menu_item_id_session) {
 //assign all the properties that belong to core class

 $output = $this->DisplayMenuItems($menu_item_id_session);
return $output
}


}

$display_items =  $display_menu_item->GetMenuItems();
echo $display_items