add to cart disappear in product page

-- url of the page with the problem --
-- HikaShop version -- : 2.3.0
-- Joomla version -- : 2.5.22
-- PHP version -- : 5.3
-- Browser(s) name and version -- : safari chrome
-- Error-message(debug-mod must be tuned on) -- :
500 - JDatabaseMySQLi::query: 1054 - Unknown column 'a.ordering' in 'order clause' SQL=SELECT DISTINCT b.* FROM hfzkc_hikashop_product AS b LEFT JOIN hfzkc_hikamarket_vendor AS hikam_vendor ON b.product_vendor_id = hikam_vendor.vendor_id WHERE b.product_published=1 AND b.product_parent_id=245 AND b.product_type = 'variant' AND (b.product_access = 'all' OR b.product_access LIKE '%,1,%') AND (hikam_vendor.vendor_published IS NULL OR hikam_vendor.vendor_published = 1) ORDER BY a.ordering ASC LIMIT 0, 20


my question is : add to cart button disappear but when ㄛ turn on the debug system, it show error message as above and add to cart button show up again, could you explain it?

ok, the problem has been solved!