Oracle之TO_DATE用法详解

    
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 //显示Two Hundred Twenty-Two    

select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day') from dual;     //星期一     
select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day',
'NLS_DATE_LANGUAGE = American') from dual;   // monday   
//设置日期语言     
ALTER SESSioN SET NLS_DATE_LANGUAGE='AMERICAN';     
//也可以这样     
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;  //注意要用TO_DATE(null)    

a_date between to_date('20011201','yyyymmdd') and to_date('20011231','yyyymmdd')     
//那么12月31号中午12点之后和12月1号的12点之前是不包含在这个范围之内的。     
//所以，当时间需要精确的时候，觉得to_char还是必要的

alter system set NLS_DATE_LANGUAGE = American     
alter session set NLS_DATE_LANGUAGE = American     
//或者在to_date中写     
select to_char(to_date('2002-08-26','yyyy-mm-dd'),
   'day','NLS_DATE_LANGUAGE = American') from dual;     
//注意我这只是举了NLS_DATE_LANGUAGE，当然还有很多，可查看     
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' )     
//查找2002-02-28至2002-02-01间除星期一和七的天数     
//在前后分别调用DBMS_UTILITY.GET_TIME, 让后将结果相减(得到的是1/100秒, 而不是毫秒).    

select months_between(to_date('01-31-1999','MM-DD-YYYY'),
to_date('12-31-1998','MM-DD-YYYY')) "MONTHS" FROM DUAL;     
//结果为：1     
select months_between(to_date('02-01-1999','MM-DD-YYYY'),
to_date('12-31-1998','MM-DD-YYYY')) "MONTHS" FROM DUAL;     
//结果为：1.03225806451613

Next_day(date, day)     
Monday-Sunday, for fORMat code DAY     
Mon-Sun, for format code DY     
1-7, for format code D    

//extract()找出日期或间隔值的字段值
SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 2:38:40') from offer     
select sysdate ,to_char(sysdate,'hh') from dual;     
 
SYSDATE               TO_CHAR(SYSDATE,'HH')     
-------------------- ---------------------     
2003-10-13 19:35:21   07     
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    
   //闰年的处理方法     
  to_char( last_day( to_date('02'    | | :year,'mmyyyy') ), 'dd' )     
   //如果是28就不是闰年 
 

   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    
   //2002-11-1 9:55:00 35786     
   //SSSSS表示5位秒数    
 

    select TO_CHAR(SYSDATE,'DDD'),sysdate from dual   
   //310  2002-11-6 10:03:51    
 

     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.
 

   //返回下个星期的日期,day为1-7或星期日-星期六,1表示星期日
   next_day(sysdate,6)是从当前开始下一个星期五。后面的数字是从星期日开始算起。     
   // 1  2  3  4  5  6  7     
   //日 一 二 三 四 五 六   
   select (sysdate-to_date('2003-12-03 12:55:45','yyyy-mm-dd hh24:mi:ss'))*24*60*60 from dual
   //日期 返回的是天 然后 转换为ss

   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

     注:oracle时间差是以天数为单位,所以换算成年月,日
      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
 

 //oracle时间加减是以天数为单位,设改变量为n,所以换算成年月,日
 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;