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在Oracle中实现各种日期处理(转)

原创 Oracle 作者:csbin 时间:2007-01-27 13:54:34 0 删除 编辑

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TO_DATE格式
  Day:   
  dd    number     12
  dy    abbreviated  fri     
  day   spelled out  friday            
  ddspth  spelled out,  ordinal  twelfth
  Month:  
  mm    number     03
  mon   abbreviated  mar
  month  spelled out  march 
  Year:             
  yy    two digits  98
  yyyy   four digits  1998  
  
  24小时格式下时间范围为: 0:00:00 - 23:59:59....
  12小时格式下时间范围为: 1:00:00 - 12:59:59 ....  
1. 日期和字符转换函数用法(to_date,to_char)
   
 
2. select to_char( to_date(222,'J'),'Jsp') from dual
  
  显示Two Hundred Twenty-Two

3. 求某天是星期几
  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','NL2006-3-22_LANGUAGE = American') from dual; 
  monday  
  设置日期语言
  ALTER SESSION SET NL2006-3-22_LANGUAGE='AMERICAN';
  也可以这样
  TO_DATE ('2002-08-26', 'YYYY-mm-dd', 'NL2006-3-22_LANGUAGE = American')
 

4. 两个日期间的天数
  select floor(sysdate - to_date('20020405','yyyymmdd')) from dual;
 


5.时间为null的用法
  select id, active_date from table1
   UNION
  select 1, TO_DATE(null) from dual;
  
  注意要用TO_DATE(null)

 
6. 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

7.日期格式冲突问题
     输入的格式要看你安装的ORACLE字符集的类型, 比如: US7ASCII, date格式的类型就是: '01-Jan-01'
  alter system set NL2006-3-22_LANGUAGE = American
     alter session set NL2006-3-22_LANGUAGE = American
  或者在to_date中写
  select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NL2006-3-22_LANGUAGE = American') from dual; 
  注意我这只是举了NL2006-3-22_LANGUAGE,当然还有很多,
  可查看
  select * from nls_session_parameters
  select * from V$NLS_PARAMETERS
 

 日期和字符转换函数用法(to_date,to_char)
     We overwrite NL2006-3-22_FORMAT into different formats for the session. 
     SQL> alter session set nls_date_format = 'DD-MON-RR'; Session altered.
     SQL> set pagesize 0
   SQL> set linesize 130
   SQL> select * from nls_session_parameters;
   NLS_LANGUAGE          AMERICAN
   NLS_TERRITORY         AMERICA
   NLS_CURRENCY          $
   NLS_ISO_CURRENCY        AMERICA
   NLS_NUMERIC_CHARACTERS     .,
   NLS_CALENDAR          GREGORIAN
   NL2006-3-22_FORMAT        DD-MON-RR
   NL2006-3-22_LANGUAGE       AMERICAN
   NLS_SORT            BINARY
   NLS_TIME_FORMAT        HH.MI.SSXFF AM
   NLS_TIMESTAMP_FORMAT      DD-MON-RR HH.MI.SSXFF AM
   NLS_TIME_TZ_FORMAT       HH.MI.SSXFF AM TZH:TZM
   NLS_TIMESTAMP_TZ_FORMAT    DD-MON-RR HH.MI.SSXFF AM TZH:TZM
   NLS_DUAL_CURRENCY       $
   NLS_COMP            BINARY

   15 rows selected.
     specify it in SQL statement:
     
    SQL> select to_date('03-SEP-1999','DD-MON-YYYY') from dual;
     03-SEP-99
    SQL> alter session set nls_date_format = 'MM-DD-YYYY';
       Session altered.
      
    SQL> select to_date('03-SEP-99','DD-MON-YY') from dual;
       TO_DATE('0
       ----------
       09-03-1999 
    SQL> alter session set nls_date_format = 'RRRR-MM-DD';
       Session altered. 
      
    SQL> select to_date('03-SEP-1999','DD-MON-YYYY') from dual;
       TO_DATE('0
       ----------
       1999-09-03 
      
  When we use TO_CHAR function, we get expected results of format from current SQL statement: 
    SQL> alter session set nls_date_format = 'MM-DD-YY';
       Session altered. 
    SQL> select to_char(sysdate,'dd-mm-yyyy') from dual;
       TO_CHAR(SYSDATE,'DD-MM-YYYY') 
       07-09-1999 
    SQL> alter session set nls_date_format = 'RR-MON-DD';
       Session altered. 
    SQL> select to_char(sysdate,'dd-mon-yy') from dual;
       TO_CHAR(SYSDATE,'DD-MON-YY') 
       07-sep-99 
    SQL> select to_char(sysdate,'dd-Mon-yy') from dual;
       TO_CHAR(SYSDATE,'DD-MON-YY') 
       07-Sep-99
8. 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).  

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

10.Next_day的用法
  Next_day(date, day)
  
  Monday-Sunday, for format code DAY   
  Mon-Sun, for format code DY     
  1-7, for format code D 
 

11.select to_char(sysdate,'hh:mi:ss') TIME from all_objects
  注意:第一条记录的TIME 与最后一行是一样的
  可以建立一个函数来处理这个问题
  create or replace function sys_date return date is 
  begin 
  return sysdate; 
  end; 
  
  select to_char(sys_date,'hh:mi:ss') from all_objects; 

12.获得小时数
     
     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
     
     获取年月日与此类似

13. 年月日的处理
  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 )
      )

 
14. 处理月份天数不定的办法
  select to_char(add_months(last_day(sysdate) +1, -2), 'yyyymmdd'),last_day(sysdate) from dual
 
16. 找出今年的天数
  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
 
17. yyyy与rrrr的区别
  'YYYY99 TO_C
  ------- ----
  yyyy 99 0099
  rrrr 99 1999
  yyyy 01 0001
  rrrr 01 2001
 
18.不同时区的处理
  select to_char( NEW_TIME( sysdate, 'GMT','EST'), 'dd/mm/yyyy hh:mi:ss') ,sysdate
  from dual; 
 
19. 5秒钟一个间隔
  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
 
20. 一年的第几天
  select TO_CHAR(SYSDATE,'DDD'),sysdate from dual 
  310 2002-11-6 10:03:51
 
21.计算小时,分,秒,毫秒
  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
  )
 
  
9i以上版本
  -----------------------------
  SQL>select to_char(systimestamp,'yyyy-mm-dd hh24:mi:ssxff') time1,
  to_char(current_timestamp) time2 from dual;
  
  TIME1             TIME2
  ----------------------------- ----------------------------------------------------------------
  2003-10-24 10:48:45.656000  24-OCT-03 10.48.45.656000 AM +08:00
  可以看到,毫秒在to_char中对应的是FF。
  
  SQL> select to_timestamp('2003-10-24 10:48:45.656000','yyyy-mm-dd hh24:mi:ssxff') from dual;
  
  TO_TIMESTAMP('2003-10-2410:48:
  -------------------------------------------------
  24-10月-03 10.48.45.656000000 上午
 

22.floor((date2-date1) /365) 作为年
    floor((date2-date1, 365) /30) 作为月
    mod(mod(date2-date1, 365), 30)作为日.

23.next_day函数
  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 
 

24.取出一个时间段中星期日星期六的天数
function weekends( p_date1 in date, p_date2 in date )
return number
as
   l_date1 date default least(p_date1,p_date2);
   l_date2 date default greatest(p_date1,p_date2);
   l_days number default trunc(l_date2-l_date1)+1;
   l_cnt  number;
begin
   select count(*) into l_cnt
    from (select rownum r 
        from all_objects where rownum <= l_days)
   where to_char(l_date1+r-1,'dy') in ( 'sat','sun' );
 
   return l_cnt;
end;

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