$total_count_obj = $db->selectObjectsBysql("select ngaythang, now() as ngayhientai from warranty where code_imei_sn ='778905V000605Z' ");
$ng_thang = strtotime($total_count_obj[0]->ngaythang);
$ng_hientai = strtotime($total_count_obj[0]->ngayhientai);
$datediff = abs($ng_hientai - $ng_thang);
$songay = floor($datediff / (60*60*24));