Oracle function : to_date and to_char

coexctxefx

　　First,here are some defination of date.
　　D :the day number of the week,example: Monday is two
  DAY :the day name ,example:Monday
  DD :  the day number of the month,from 0 to 31
  DDD : the day number of the year, from 0 to 365
  DY :  the day name for shot.
  IW :  the week number of the year(ISO standard)
  IYYY :  the year of ISO standard
  YYYY :  the year
  YYY,YY,Y :  the last three,two,one number of the year
  HH :  stand for the hour,0-12
  HH24 :  stand for the hour,0-24
  MI :  minute
  SS :  second
  MM :  month
  Mon : the month name for short
  Month :  the month name
  W :  the week number of the month
  WW : the week number of year
　　then some examples on oracle:

select sysdate,to_char(sysdate,'yyyy-mm-dd hh:mi:ss') from dual
2009-12-17 16:40:51  2009-12-17 04:40:51
select sysdate,to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual
2009-12-17 16:40:21  2009-12-17 16:40:21
select sysdate,sysdate - interval '7' minute from dual
2009-12-17 16:37:14  2009-12-17 16:30:14
select sysdate,sysdate - interval '1' day from dual
2009-12-17 16:58:31  2009-12-16 16:58:31
select sysdate,to_char(sysdate,'yyyy-ddd hh:mi:ss') from dual
2009-12-17 16:53:28  2009-351 16:53:28
select sysdate,to_char(sysdate,'yyyy-dy hh24:mi:ss') from dual
2009-12-17 16:56:27  2009-星期四 16:56:27
insert into t_log values(4,to_date('2007-10-10 15:32:32','yyyy-MM-dd hh24:mi:ss'),'log of 2007')