php beginner: handling array in Joomla module

Newbie in php, I am trying to create a module to extract orders from Joomla database and plot monthly results as a yearly curve. I am trying to store first the products in an array, followed by a monthly number of orders.

Database extraction is ok and I created a first array containing the product names and for each product, I'd like to create an array containing its 12 monthly quantities.

I created the product names array as below:

foreach ($products as $pr)
    $results[] = $pr->name;
    

and the quantities array in the products loop as below:

foreach ($quantities as $quant) 
    $quant_array[] = $quant->number;

Now, how can I merge those two arrays (and also how to read data afterwards) so that the results looks like

prod_A-->1
         1
         2
       ...
prod_B-->2
         3
         5
       ...
prod_C-->3
         4
         2
       ...

Helper code is herebelow, obviously not finished:

public static function getProduits($params)
        {
        $user   = JFactory::getUser();
        $userId = (int) $user->get('id');
        
        // Obtain a database connection
        $db = JFactory::getDbo();
        $query="select `name` as prodname, product_id from #__jshopping_products where product_publish=1 order by `name`";
        // Prepare the query
        $db->setQuery($query);
        // Loading products.
        $prod = $db->loadObjectList();
        
        foreach ($prod as $pr)
            {
            $results[] = $pr->prodname;

            $query2 = "SELECT count(product_quantity) as number, month(#__jshopping_orders.order_date) as month from #__jshopping_order_item join #__jshopping_orders on #__jshopping_orders.order_id=#__jshopping_order_item.order_id " .
                      "where #__jshopping_order_item.order_id in (select order_id FROM #__jshopping_orders where user_id=" . $userId . " and year(#__jshopping_orders.order_date)=2022 order by order_date desc) " .
                      "and product_id=" . $pr->product_id . " group by month(order_date) order by month(order_date) desc";

            // Prepare the query
            $db->setQuery($query2);
            // Loading data
            $amounts = $db->loadObjectList();

            foreach ($amounts as $quant) 
                $quant_array[] = $quant->number;    
            }
            
            **/// This is where I'd like to merge results within one array ($results)
            // like $results['product']['count']**
        
        return ($results);
        }
}

$results being passed to the template file for output

It is probably a trivial task but as I said, I am a php beginner...

Thank you!

Revisiting this question, I succeeded creating a single query to achieve this. When I test results within the helper file with echo statements, it displays ok. However, when I try to get the values in the default.php output template file, I just get nothing, meaning that I probably have an issue with either the variable return or something else which I don't see, being a real php newbie...

Here's how I declared my module entry point:

<?php
// No direct access defined('_JEXEC') or die; 
// Include the syndicate functions only once
require_once dirname(__FILE__) . '/helper.php';
global $prod;
$prod = modProduitsHelper::getProduits($params);
require JModuleHelper::getLayoutPath('mod_produits');
?>

I know I should not use a global declaration but I tried :-)

Helper file is ok and looks like this:

<?php
/**
 * Helper class for module stats
 */
class modProduitsHelper
{
/**
 *
 * @param   array  $params An object containing the module parameters
 *
 * @access public
 */    
    public static function getProduits($params)
        {
        $user   = JFactory::getUser();
        $userId = (int) $user->get('id');
        
        // Obtain a database connection
        $db = JFactory::getDbo();
        $query="SELECT
              product_name as nom,
              sum(if(month(order_date) = 1, product_quantity, 0)) as Janv,
              sum(if(month(order_date) = 2, product_quantity, 0)) as Feb,
              sum(if(month(order_date) = 3, product_quantity, 0)) as Mar,
              sum(if(month(order_date) = 4, product_quantity, 0)) as Apr,
              sum(if(month(order_date) = 5, product_quantity, 0)) as May,
              sum(if(month(order_date) = 6, product_quantity, 0)) as Jun,
              sum(if(month(order_date) = 7, product_quantity, 0)) as Jul,
              sum(if(month(order_date) = 8, product_quantity, 0)) as Aug,
              sum(if(month(order_date) = 9, product_quantity, 0)) as Sep,
              sum(if(month(order_date) = 10, product_quantity, 0)) as Oct,
              sum(if(month(order_date) = 11, product_quantity, 0)) as Nov,
              sum(if(month(order_date) = 12, product_quantity, 0)) as `Dec`
            FROM vpkbb_jshopping_order_item join vpkbb_jshopping_orders on vpkbb_jshopping_orders.order_id=vpkbb_jshopping_order_item.order_id  
            WHERE user_id = 398
            AND year(order_date) = 2022
            group by product_name
            order by product_name;";
        // Prepare the query
        $db->setQuery($query);
        // Chargement des produits.
        $prod = $db->loadObjectList();
        
        return ($prod);
        }
}?>

and, finally, my default.php template file looks for now just like this:

<?php 
// No direct access
defined('_JEXEC') or die;   

foreach ($prod as $pr)
    echo $pr->nom . ' ' . $pr->Jan . ' ' . $pr->Feb . ' ' . $pr->Mar . ' ' . $pr->Apr . ' ' . $pr->May . ' ' . $pr->Jun . ' ' . $pr->Jul . ' ' . $pr->Aug . ' ' . $pr->Sep . ' ' . $pr->Oct . ' ' . $pr->Nov . ' ' . $pr->Dec . '<br />';?> 

I thought I had my Xmas present, but it looks like I don't, so if anybody could point me to what I do wrong, this would save this miserable attempt to achieve my goal.

Thx