oracle中to_date详细用法示例(oracle日期格式转换)

飞奔的炮台

TO_DATE格式(以时间:2007-11-02 13:45:25为例)
1. 日期和字符转换函数用法（to_date,to_char）

select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') as nowTime from dual;   //日期转化为字符串  
select to_char(sysdate,'yyyy')  as nowYear   from dual;   //获取时间的年  
select to_char(sysdate,'mm')  as nowMonth  from dual;   //获取时间的月  
select to_char(sysdate,'dd')  as nowDay  from dual;   //获取时间的日  
select to_char(sysdate,'hh24')  as nowHour   from dual;   //获取时间的时  
select to_char(sysdate,'mi')  as nowMinute from dual;   //获取时间的分  
select to_char(sysdate,'ss')  as nowSecond from dual;   //获取时间的秒

2. 字符串和时间互转

select to_date('2004-05-07 13:23:44','yyyy-mm-dd hh24:mi:ss') from dual
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.月份差

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

8.查询特殊条件天数

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. 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;   
//结果为：1   
select months_between(to_date('02-01-1999','MM-DD-YYYY'),
to_date('12-31-1998','MM-DD-YYYY')) "MONTHS" FROM DUAL;   
//结果为：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.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   
select sysdate ,to_char(sysdate,'hh') from dual;   
SYSDATE         TO_CHAR(SYSDATE,'HH')   
-------------------- ---------------------   
2003-10-13 19:35:21   07  
select sysdate ,to_char(sysdate,'hh24') from dual;   
SYSDATE         TO_CHAR(SYSDATE,'HH24')   
-------------------- -----------------------   
2003-10-13 19:35:21   19

12.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
    )
  )

13.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

14.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

15.yyyy与rrrr的区别

YYYY99  TO_C   
------- ----   
yyyy 99 0099  
rrrr 99 1999  
yyyy 01 0001  
rrrr 01 2001

16.不同时区的处理

select to_char( NEW_TIME( sysdate, 'GMT','EST'), 'dd/mm/yyyy hh:mi:ss') ,
sysdate   from dual;

17. 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

18.一年的第几天

select TO_CHAR(SYSDATE,'DDD'),sysdate from dual   
//310  2002-11-6 10:03:51

19.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
   ) SELECT
   *
   FROM
   tabname
   ORDER BY
   DECODE (MODE, 'FIFO', 1 ,- 1) * TO_CHAR (rq, 'yyyymmddhh24miss')
//   floor((date2-date1) /365) 作为年   
//  floor((date2-date1, 365) /30) 作为月   
//  d(mod(date2-date1, 365), 30)作为日.

20.next_day函数

//返回下个星期的日期,day为1-7或星期日-星期六,1表示星期日
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 dual
//日期 返回的是天 然后 转换为ss

21,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

22,trunc[截断到最接近的日期,单位为天] ,返回的是日期类型

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

23,返回日期列表中最晚日期

select greatest('01-1月-04','04-1月-04','10-2月-04') from dual

24.计算时间差

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

25.更新时间

//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

26.查找月的第一天,最后一天

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;