TO_DATE格式(以時間:2007-11-02 13:45:25為例)?
Year:?
yy two digits 兩位年 顯示值:07
yyy three digits 三位年 顯示值:007
yyyy four digits 四位年 顯示值:2007
Month:?
mm number 兩位月 顯示值:11
mon abbreviated 字符集表示 顯示值:11月,若是英文版,顯示nov?
month spelled out 字符集表示 顯示值:11月,若是英文版,顯示novembe
Day:?
dd number 當月第幾天 顯示值:02
ddd number 當年第幾天 顯示值:02
dy abbreviated 當周第幾天簡寫 顯示值:星期五,若是英文版,顯示fri
day spelled out 當周第幾天全寫 顯示值:星期五,若是英文版,顯示friday?
ddspth spelled out, ordinal twelfth

Hour:
hh two digits 12小時進制 顯示值:01
hh24 two digits 24小時進制 顯示值:13

Minute:
mi two digits 60進制 顯示值:45

Second:
ss two digits 60進制 顯示值:25

其它
Q digit 季度 顯示值:4
WW digit 當年第幾周 顯示值:44
W digit 當月第幾周 顯示值:1

24小時格式下時間范圍為： 0:00:00 - 23:59:59....?
12小時格式下時間范圍為： 1:00:00 - 12:59:59 ....

1. 日期和字符轉換函數用法（to_date,to_char）

select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') as nowTime from dual; //日期轉化為字符串?
select to_char(sysdate,'yyyy') as nowYear from dual; //獲取時間的年?
select to_char(sysdate,'mm') as nowMonth from dual; //獲取時間的月?
select to_char(sysdate,'dd') as nowDay from dual; //獲取時間的日?
select to_char(sysdate,'hh24') as nowHour from dual; //獲取時間的時?
select to_char(sysdate,'mi') as nowMinute from dual; //獲取時間的分?
select to_char(sysdate,'ss') as nowSecond from dual; //獲取時間的秒
select to_date('2004-05-07 13:23:44','yyyy-mm-dd hh24:mi:ss') from dual//

2.?
select to_char( to_date(222,'J'),'Jsp') from dual?

顯示Two Hundred Twenty-Two

3.求某天是星期幾?
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?
設置日期語言?
ALTER SESSION SET NLS_DATE_LANGUAGE='AMERICAN';?
也可以這樣?
TO_DATE ('2002-08-26', 'YYYY-mm-dd', 'NLS_DATE_LANGUAGE = American')

4. 兩個日期間的天數?
select floor(sysdate - to_date('20020405','yyyymmdd')) from dual;

5. 時間為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.月份差?
a_date between to_date('20011201','yyyymmdd') and to_date('20011231','yyyymmdd')?
那么12月31號中午12點之后和12月1號的12點之前是不包含在這個范圍之內的。?
所以，當時間需要精確的時候，覺得to_char還是必要的

7. 日期格式沖突問題?
輸入的格式要看你安裝的ORACLE字符集的類型, 比如: US7ASCII, date格式的類型就是: '01-Jan-01'?
alter system set NLS_DATE_LANGUAGE = American?
alter session set NLS_DATE_LANGUAGE = American?
或者在to_date中寫?
select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = American') from dual;?
注意我這只是舉了NLS_DATE_LANGUAGE，當然還有很多，?
可查看?
select * from nls_session_parameters?
select * from V$NLS_PARAMETERS

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間除星期一和七的天數?
在前后分別調用DBMS_UTILITY.GET_TIME, 讓后將結果相減(得到的是1/100秒, 而不是毫秒).

9. 查找月份?
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：第一條記錄的TIME 與最后一行是一樣的?
可以建立一個函數來處理這個問題?
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.獲得小時數?
extract()找出日期或間隔值的字段值
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