我如何将我的数组结果加在一起

Question

如何获得我的数组的结果？
我试过了：

if (isset($_SESSION["cart_array"]) && is_array($_SESSION["cart_array"])) {
    foreach ($_SESSION["cart_array"] as $each_item) {
        $id  = $each_item["item_id"];
        $qty = $each_item["quantity"];
        $sql = mysql_query("SELECT * FROM promo WHERE code='$id' LIMIT 1");
        while ($row = mysql_fetch_array($sql)) {
            $price     = $row["price"];
            $cartTotal = $price * $qty;
            echo "$cartTotal,";
        }
    }
}

提前致谢。