时间查询

SELECT * FROM `subject` WHERE `postdate` >= '2015-03-06 ' AND `postdate` < '2015-03-07'  

mysql  默认 的查询时间为： 

SELECT * FROM `subject` WHERE `postdate` >= '2015-03-06 00:00:00 ' AND `postdate` < '2015-03-07 00:00:00'