checkout qty不会在结帐时更新小计

Question

Hey I have a problem with a site in PHP where if you change the quantity in the checkout the subtotal doesnt change. Im not very competent with PHP so it might be something simple. Here is the code for updating qty;

<?php include_once($_SERVER["DOCUMENT_ROOT"].'/vuengine/viewerlib.php'); ?>

<?php
$listing_num         = $_REQUEST['pd_id'];
$listing_qty         = $_REQUEST['pd_qty'];
$order_num           = $_COOKIE['ordernum'];

echo $order_num;

//Get order details
$order_details     = mysql_select('orders', 'num='.$order_num);
$listings_subtotal = $order_details[0]['listings_subtotal'];

//Get listing details
$listing_details = mysql_select('listings', 'num='.$listing_num);
$seller_num      = $listing_details[0]['member_num'];

//Update order with new shipping
//Get orders_sellers_items unit_price and qty
$order_sellers_item_details = mysql_select('orders_sellers_items',        
'order_num='.$order_num.' AND listing_num='.$listing_num);

//Get unit price
$unit_price     = $order_sellers_item_details[0]['unit_price'];
$qty            = $order_sellers_item_details[0]['qty'];
$shipping_num   = $order_sellers_item_details[0]['shipping_num'];
$shipping_price = $order_sellers_item_details[0]['shipping_price'];

 //Get shipping price
$shipping_price = mysql_select('shipping_rates', 'num='.$shipping_num);
$shipping_price = $shipping_price[0]['charge'];

$new_shipping_total = $shipping_price*$listing_qty;

$new_subtotal = ($unit_price*$listing_qty);

//Update orders_sellers_items with new subtotal
mysql_update('orders_sellers_items', null, 'order_num='.$order_num.' AND     
listing_num='.$listing_num, array('subtotal' => $new_subtotal+$new_shipping_total, 
'qty' => $listing_qty, 'shipping_price' => $shipping_price));


//Update order with new listing_subtotal
$orders_items = mysql_select('orders_sellers_items','order_num='.$order_num);   
$order_subtotal    = 0;    
$shipping_subtotal = 0;
foreach($orders_items as $order_item){
$order_subtotal    +=$order_item['unit_price']*$order_item['qty'];
$shipping_subtotal +=$order_item['shipping_price']*$order_item['qty'];
}

mysql_update('orders', $order_num, null,     
array('listings_subtotal'=>$order_subtotal,     'shipping_subtotal' => 
$shipping_subtotal, 'total' => $order_subtotal+$shipping_subtotal, 'updatedDate=' => 
'NOW()'));

//Get orders_sellers_items for order and seller
$orders_items_seller =     
mysql_select('orders_sellers_items','order_num='.$order_num.'     AND     
seller_num='.$seller_num);  
$order_subtotal2     = 0;
$order_shipping      = 0;
foreach($orders_items_seller as $order_item_seller){
$order_subtotal2 += $order_item_seller['unit_price']*$order_item_seller['qty'];
$order_shipping  += $order_item_seller['shipping_price']*$order_item_seller['qty'];
}

//Update orders_sellers table with new subtotal 
mysql_update('orders_sellers', null, 'order_num='.$order_num.' AND
seller_num='.$seller_num, array('listing_subtotal' => $order_subtotal2, 
'shipping_subtotal' => $order_shipping, 'seller_total' => 
$order_subtotal2+$order_shipping)); 

echo json_encode(array('subtotal' => number_format($new_subtotal+    
($shipping_price*$listing_qty),2), 'cart_total' => 
number_format($order_subtotal+$shipping_subtotal,2)));
?>