oracle中时间字段查询

一.TimeStamp类型字段:

   

select calen_id, cdate, day_sign, month_sign, year_sign, week, cur_day
  from bs_Calendar
 where cdate >= to_timestamp('2007-11-03 00:00:00.0','yyyy-mm-dd HH24:mi:ss.ff')
   and to_char(cdate, 'dd') = '3'

 

select calen_id, cdate, day_sign, month_sign, year_sign, week, cur_day
  from bs_Calendar
 where cdate >= to_timestamp('2007-11-03 00:00:00.0','yyyy-mm-dd HH24:mi:ss.ff')
   and  cast(to_char(cdate, 'dd') as number )  = '3'

 

    语句一查询不出任何记录.而语句二就可以达到目的,原因在于oracle做了数据类型的隐式转换.