zen_get_products_stock($products_id)
该函数主要通过商品的ID返回该商品的库存量
主要查询了 products 表。在includes/database_tables.php中定义：
define(‘TABLE_PRODUCTS’, DB_PREFIX . ‘products’);function zen_get_products_stock($products_id) {
global $db;
$products_id = zen_get_prid($products_id);
$stock_query = "select products_quantity
from " . TABLE_PRODUCTS . "
where products_id = '" . (int)$products_id . "'";
$stock_values = $db->Execute($stock_query);
return $stock_values->fields['products_quantity'];
}