$sql_order_detail = 'SELECT `id_order_detail`, `product_id`, `product_quantity`, `unit_price_tax_incl` FROM '._DB_PREFIX_.'order_detail WHERE `id_order` = ' . $id_order;

$order_details = Db::getInstance()->ExecuteS($this->sql_order_detail, $array = true, $use_cache = 0);

SELECT `id_order_detail`, `product_id`, `product_quantity`, `unit_price_tax_incl` FROM ps_order_detail WHERE `id_order` = 24

stderr: Db->executeS() must be used only with select, show, explain or describe queries,