oracle 查询时间

写法有很多种，例如下面的：
方法一：select * from dual where time between to_date('2012-06-18 00:00:00','yyyy-mm-dd hh24:mi:ss')  and to_date('2012-06-18 23:59:59','yyyy-mm-dd hh24:mi:ss');
方法二：select * from dual where to_char(time,'yyyy-mm-dd')='2012-06-18';
方法三：select * from dual where trunc(time)=to_date('2012-06-18','yyyy-mm-dd');