TO_DATE格式
Day:
dd number 12
dy abbreviatedfri
dayspelled outfriday
ddspth spelled out, ordinal twelfth
Month:
mm number 03
monabbreviatedmar
monthspelled outmarch
Year:
yy twodigits98
yyyy fourdigits 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;
注重要用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;
注重我这只是举了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_TERRITORYAMERICA
NLS_CURRENCY $
NLS_ISO_CURRENCY AMERICA
NLS_NUMERIC_CHARACTERS .,
NLS_CALENDAR GREGORIAN
NLS_DATE_FORMATDD-MON-RR
NLS_DATE_LANGUAGEAMERICAN
NLS_SORT BINARY
NLS_TIME_FORMATHH.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_FORMATDD-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 fromcurrent 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
注重：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;
SYSDATETO_CHAR(SYSDATE,'HH')
-------------------- ---------------------
2003-10-13 19:35:2107
SQL select sysdate ,to_char(sysdate,'hh24')from dual;
SYSDATETO_CHAR(SYSDATE,'HH24')
-------------------- -----------------------
2003-10-13 19:35:2119
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(tr