如何对购物篮实行折扣

Question

我正在尝试为每对2项商品（每本售价£1.50）打折，但我似乎无法掌握。我从“折扣”和“购物篮”的两个SQL查询/表中得出结果。这是我尝试过的以下内容：

$discount_count[] = 0;
$i = 0;
while ($row2 = mysql_fetch_array($data_set2)) {                                 
  if ($row['product'] == $row2['product']) {
  foreach ($row2 as $current_row) {

     $actual_price = $row['product_cost'] * $row2['quantity'];
     $discount_total = round(($actual_price - ($actual_price * ($row2['discount_percent'] / 100))), 2);
     $total_price = $discount_total / $row2['quantity'] * $row['quantity'];
     $product_total = $row['product_cost'] * $row['quantity'];

     if ($i % 2 && $total_price * $row2['quantity'] > $row['product_cost'] * $row2['quantity']){
         echo "<br /><br />actual price per 2: £" . $actual_price;
         echo "<br />discount total: £" . $discount_total;
         echo "<br />actual minus discount: £";
         echo $actual_price - $discount_total;
         echo "<br />total price: £" . $total_price;
         echo "<br />product cost: £" . $product_total;

         $discount_count[] = $actual_price - $discount_total;
     }
         $i++;
         }
       }
    }