oracle 日期格式化(yyyymmdd)及常规日期计算大全

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 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       

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    

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' )   

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;      

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    

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  

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      

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    

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 

)      

)    

'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    

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      

)

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 ddual

日期 返回的是天 然后 转换为ss

24,round[舍入到最接近的日期](day:舍入到最接近的星期日)

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

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

注: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;