我有一个sql查询，它返回3个最新的格式，但在我将fin\u date列类型从string更改为date并使用特定格式后，它就不起作用了：

$today = JFactory::getDate()->toFormat('%d/%m/%Y');
   // echo $today==> 18/12/2018

$query =  "SELECT p.fin_date, pfr.product_name, p.ville"
             ." FROM #__virtuemart_products as p"
             ." LEFT JOIN #__virtuemart_products_fr_fr as pfr on pfr.virtuemart_product_id = p.virtuemart_product_id"
             ." WHERE p.published = 1   AND  p.product_parent_id != 0 AND str_to_date(p.fin_date,'%d/%m/%Y') >= $today "
             ." LIMIT 4 "
             ;

甚至我把它改成：

$query =  "SELECT str_to_date(p.fin_date,'%d/%m/%Y'), pfr.product_name, p.ville"
             ." FROM #__virtuemart_products as p"
             ." LEFT JOIN #__virtuemart_products_fr_fr as pfr on pfr.virtuemart_product_id = p.virtuemart_product_id"
             ." WHERE p.published = 1   AND  p.product_parent_id != 0 AND str_to_date(p.fin_date,'%d/%m/%Y') >= $today "
             ." LIMIT 4 "
             ;