select to_char(sysdate,'yy-mm-dd hh24:mi:ss') from dual  //显示：08-11-07 13:22:42

select to_date('2005-12-25,13:25:59','yyyy-mm-dd,hh24:mi:ss') from dual //显示：2005-12-25 13:25:59

select sysdate,sysdate - interval '7' MINUTE from dual 

select sysdate - interval '7' hour from dual 

select sysdate - interval '7' day from dual 

select sysdate,sysdate - interval '7' month from dual 

select sysdate,sysdate - interval '7' year from dual 

select sysdate,sysdate - 8*interval '7' hour from dual

select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') as nowTime from dual;  //日期转化为字符串  
select to_char(sysdate,'yyyy') as nowYear  from dual;  //获取时间的年  
select to_char(sysdate,'mm')  as nowMonth from dual;  //获取时间的月  
select to_char(sysdate,'dd')  as nowDay  from dual;  //获取时间的日  
select to_char(sysdate,'hh24') as nowHour  from dual;  //获取时间的时  
select to_char(sysdate,'mi')  as nowMinute from dual;  //获取时间的分  
select to_char(sysdate,'ss')  as nowSecond from dual;  //获取时间的秒

select to_date('2004-05-07 13:23:44','yyyy-mm-dd hh24:mi:ss')  from dual//

select to_char( to_date(222,'J'),'Jsp') from dual   

select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day') from dual;   

select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = American') from dual;    

ALTER SESSION SET NLS_DATE_LANGUAGE='AMERICAN'; 

TO_DATE ('2002-08-26', 'YYYY-mm-dd', 'NLS_DATE_LANGUAGE = American')  

select floor(sysdate - to_date('20020405','yyyymmdd')) from dual;  

select id, active_date from table1   
UNION   
select 1, TO_DATE(null) from dual; 

a_date between to_date('20011201','yyyymmdd') and to_date('20011231','yyyymmdd')   

alter system set NLS_DATE_LANGUAGE = American   
alter session set NLS_DATE_LANGUAGE = American  

select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = American') from dual;  

select * from nls_session_parameters   
select * from V$NLS_PARAMETERS  

  select count(*)   
  from ( select rownum-1 rnum   
    from all_objects   
    where rownum <= to_date('2002-02-28','yyyy-mm-dd') - to_date('2002-   
    02-01','yyyy-mm-dd')+1   
   )   
  where to_char( to_date('2002-02-01','yyyy-mm-dd')+rnum-1, 'D' )   
    not in ( '1', '7' )  

select months_between(to_date('01-31-1999','MM-DD-YYYY'),to_date('12-31-1998','MM-DD-YYYY')) "MONTHS" FROM DUAL;      
select months_between(to_date('02-01-1999','MM-DD-YYYY'),to_date('12-31-1998','MM-DD-YYYY')) "MONTHS" FROM DUAL;   

Next_day(date, day)  

select to_char(sysdate,'hh:mi:ss') TIME from all_objects   

  create or replace function sys_date return date is   
  begin   
  return sysdate;   
  end;   
  
  select to_char(sys_date,'hh:mi:ss') from all_objects;  

  SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 2:38:40') from offer   
  SQL> select sysdate ,to_char(sysdate,'hh') from dual;   
  
  SYSDATE TO_CHAR(SYSDATE,'HH')   
  -------------------- ---------------------   
  2003-10-13 19:35:21 07   
  
  SQL> select sysdate ,to_char(sysdate,'hh24') from dual;   
  
  SYSDATE TO_CHAR(SYSDATE,'HH24')   
  -------------------- -----------------------   
  2003-10-13 19:35:21 19   

  select older_date,   
    newer_date,   
    years,   
    months,   
    abs(   
    trunc(   
     newer_date-   
     add_months( older_date,years*12+months )   
    )   
    ) days 
    
  from ( select   
    trunc(months_between( newer_date, older_date )/12) YEARS,   
    mod(trunc(months_between( newer_date, older_date )),12 ) MONTHS,   
    newer_date,   
    older_date   
    from ( 
       select hiredate older_date, add_months(hiredate,rownum)+rownum newer_date   
       from emp 
       )   
   )   

select to_char(add_months(last_day(sysdate) +1, -2), 'yyyymmdd'),last_day(sysdate) from dual 

 select add_months(trunc(sysdate,'year'), 12) - trunc(sysdate,'year') from dual  

  to_char( last_day( to_date('02'  | | :year,'mmyyyy') ), 'dd' )  

  'YYYY99 TO_C   
  ------- ----   
  yyyy 99 0099   
  rrrr 99 1999   
  yyyy 01 0001   
  rrrr 01 2001   

select to_char( NEW_TIME( sysdate, 'GMT','EST'), 'dd/mm/yyyy hh:mi:ss') ,sysdate from dual;  

Select TO_DATE(FLOOR(TO_CHAR(sysdate,'SSSSS')/300) * 300,'SSSSS') ,TO_CHAR(sysdate,'SSSSS') from dual  

select TO_CHAR(SYSDATE,'DDD'),sysdate from dual

  select Days, A,   
   TRUNC(A*24) Hours,   
   TRUNC(A*24*60 - 60*TRUNC(A*24)) Minutes,   
   TRUNC(A*24*60*60 - 60*TRUNC(A*24*60)) Seconds,   
   TRUNC(A*24*60*60*100 - 100*TRUNC(A*24*60*60)) mSeconds   
  from   
  (   
   select   
   trunc(sysdate) Days,   
   sysdate - trunc(sysdate) A   
   from dual   
  )   
  select * from tabname   
  order by decode(mode,'FIFO',1,-1)*to_char(rq,'yyyymmddhh24miss');   
  
  //   
  floor((date2-date1) /365) 作为年   
  floor((date2-date1, 365) /30) 作为月   
  d(mod(date2-date1, 365), 30)作为日.

select  (sysdate-to_date('2003-12-03 12:55:45','yyyy-mm-dd hh24:mi:ss'))*24*60*60 from ddual

  select sysdate S1,
  round(sysdate) S2 ,
  round(sysdate,'year') YEAR,
  round(sysdate,'month') MONTH ,
  round(sysdate,'day') DAY from dual

  select sysdate S1,           
   trunc(sysdate) S2,         //返回当前日期,无时分秒
   trunc(sysdate,'year') YEAR,    //返回当前年的1月1日,无时分秒
   trunc(sysdate,'month') MONTH ,   //返回当前月的1日,无时分秒
   trunc(sysdate,'day') DAY      //返回当前星期的星期天,无时分秒
  from dual

 select greatest('01-1月-04','04-1月-04','10-2月-04') from dual

select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))/365) as spanYears from dual    //时间差-年
   select ceil(moths_between(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))) as spanMonths from dual    //时间差-月
   select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))) as spanDays from dual       //时间差-天
   select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))*24) as spanHours from dual     //时间差-时
   select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))*24*60) as spanMinutes from dual  //时间差-分
   select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))*24*60*60) as spanSeconds from dual //时间差-秒

   select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss'),to_char(sysdate+n*365,'yyyy-mm-dd hh24:mi:ss') as newTime from dual    //改变时间-年
   select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss'),add_months(sysdate,n) as newTime from dual                 //改变时间-月
   select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss'),to_char(sysdate+n,'yyyy-mm-dd hh24:mi:ss') as newTime from dual      //改变时间-日
   select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss'),to_char(sysdate+n/24,'yyyy-mm-dd hh24:mi:ss') as newTime from dual     //改变时间-时
   select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss'),to_char(sysdate+n/24/60,'yyyy-mm-dd hh24:mi:ss') as newTime from dual   //改变时间-分
   select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss'),to_char(sysdate+n/24/60/60,'yyyy-mm-dd hh24:mi:ss') as newTime from dual  //改变时间-秒

   SELECT Trunc(Trunc(SYSDATE, 'MONTH') - 1, 'MONTH') First_Day_Last_Month,
    Trunc(SYSDATE, 'MONTH') - 1 / 86400 Last_Day_Last_Month,
    Trunc(SYSDATE, 'MONTH') First_Day_Cur_Month,
    LAST_DAY(Trunc(SYSDATE, 'MONTH')) + 1 - 1 / 86400 Last_Day_Cur_Month
  FROM dual;