开发进行时...

出自：http://www.cnoug.org/viewthread.php?tid=1976&highlight=

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','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')

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 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

日期和字符转换函数用法（to_date,to_char）
We overwrite NLS_DATE_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
NLS_DATE_FORMAT DD-MON-RR
NLS_DATE_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;