1.日期时间间隔操作

当前时间减去7分钟的时间
select sysdate,sysdate - interval '7' MINUTE from dual

当前时间减去7小时的时间
select sysdate - interval '7' hour from dual

当前时间减去7天的时间
select sysdate - interval '7' day from dual

当前时间减去7月的时间
select sysdate,sysdate - interval '7' month from dual

当前时间减去7年的时间
select sysdate,sysdate - interval '7' year from dual

时间间隔乘以一个数字
select sysdate,sysdate - 8 *interval '2' hour from dual

2.日期到字符操作

select sysdate,to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual

select sysdate,to_char(sysdate,'yyyy-mm-dd hh:mi:ss') from dual

select sysdate,to_char(sysdate,'yyyy-ddd hh:mi:ss') from dual

select sysdate,to_char(sysdate,'yyyy-mm iw-d hh:mi:ss') from dual
参考oracle的相关关文档(ORACLE901DOC/SERVER.901/A90125/SQL_ELEMENTS4.HTM#48515)

3. 字符到日期操作

select to_date('2003-10-17 21:15:37','yyyy-mm-dd hh24:mi:ss') from dual

具体用法和上面的to_char差不多。

4. trunk/ ROUND函数的使用

select trunc(sysdate ,'YEAR') from dual

select trunc(sysdate ) from dual

select to_char(trunc(sysdate ,'YYYY'),'YYYY') from dual

5.oracle有毫秒级的数据类型

--返回当前时间 年月日小时分秒毫秒

select to_char(current_timestamp(5),'DD-MON-YYYY HH24:MI:SSxFF') from dual;

--返回当前 时间的秒毫秒，可以指定秒后面的精度(最大=9)

select to_char(current_timestamp(9),'MI:SSxFF') from dual;

6.计算程序运行的时间(ms)

declare
  type rc is ref cursor;
  l_rc rc;
  l_dummy all_objects.object_name%type;
  l_start number default dbms_utility.get_time;
begin
  for I in 1 .. 1000
   loop
    open l_rc for
     'select object_name from all_objects ' ||
     'where object_id = ' || i;
    fetch l_rc
      into l_dummy;
    close l_rc;
  end loop;
  dbms_output.put_line
  (round((dbms_utility.get_time - l_start) / 100, 2) ||
   ' seconds...');
end;

7、add_months()用于从一个日期值增加或减少一些月份

1〉获得若干分钟前的时间
select sysdate,sysdate - N/(60*24) from dual;
或者
select sysdate,sysdate - interval 'N' minute from dual

2〉获得若干分钟后的时间 s
elect sysdate,sysdate + N/(60*24) from dual;
或者
select sysdate,sysdate + interval 'N' minute from dual

注释："N"表示需要减去或者加上的分钟数

3〉获得若干秒前的时间 s
elect sysdate,sysdate - N*0.00001 from dual;
或者
select sysdate,sysdate - N/(60*60*24) from dual;
或者
select sysdate,sysdate - interval 'N' second from dual

4〉获得若干秒后的时间
select sysdate,sysdate + N*0.00001 from dual;
或者
select sysdate,sysdate - N/(60*60*24) from dual;
或者
select sysdate,sysdate + interval 'N' second from dual

注释："N"表示需要减去或者加上的秒数
注释：N*0.00001 等价于 N/(60*60*24)

5〉获得若干小时前的时间
select sysdate,sysdate - N*/24 from dual;
或者
select sysdate,sysdate - interval 'N' hour from dual

6〉获得若干小时后的时间
 select sysdate,sysdate + N*/24 from dual;
或者
select sysdate,sysdate + interval 'N' hour from dual

注释："N"表示需要减去或者加上的小时数

7〉获得若干月之后同一时间
select sysdate,add_months(sysdate,N) from dual;
或者
select sysdate,sysdate + interval 'N' month from dual

8〉获得若干月之前的同一时间
select sysdate,add_months(sysdate,-N) from dual;
或者
select sysdate,sysdate - interval 'N' month from dual

注释："N"表示需要减去或者加上的月数

9〉获得某个日期所在月份的第一天
select sysdate,trunc(sysdate,'mm') from dual;

10〉获得某个日期所在年的第一天
select sysdate,trunc(sysdate,'yyyy') from dual;
或者
select sysdate,to_date(to_char((to_number(to_char(sysdate,'yyyy')) * 100 + 1) * 100 + 1),'yyyymmdd') from dual

11〉获得某个日期所在年的最后一天
select sysdate,to_date((to_char(sysdate,'yyyy') || '1231'),'yyyymmdd') from dual;
或者
select sysdate,to_date(to_char((to_number(to_char(sysdate,'yyyy'))* 100 + 12) * 100 + 31),'yyyymmdd') from dual

12〉获得某个日期所在月份的最后一天
select sysdate,last_day(sysdate) from dual;

13〉获得两个日期之间的时数
select t.intime,t.outtime,trunc(24*(t.outtime-t.intime)) from hr_carding t

14〉获得两个日期之间的天数
select t.begintime,t.endtime,trunc(t.endtime-t.begintime) from hr_absence t

15〉获得若干天前的时间 s
elect sysdate,sysdate - N from dual;
或者
select sysdate,sysdate - interval 'N' day from dual

16〉获得若干天后的时间
select sysdate,sysdate + N from dual;
或者
select sysdate,sysdate + interval 'N' day from dual

注释："N"表示需要减去或者加上的天数

17〉获得若干年前的时间
select sysdate,add_months(sysdate,-12*N) from dual;
或者
select sysdate,sysdate - interval 'N' year from dual

16〉获得若干年后的时间
select sysdate,add_months(sysdate,12*N) from dual;
或者
select sysdate,sysdate + interval 'N' year from dual

注释："N"表示需要减去或者加上的年数

17〉相隔若干小时的时间
select sysdate,sysdate - M * interval 'N' hour from dual

18〉检索出某一个日期所在月份的所有天信息

select trunc(to_date('X', 'yyyymmdd'), 'mm')
  from dual
union all
select trunc(to_date('X', 'yyyymmdd'), 'mm') + rownum
  from dual
connect by rownum <= (last_day(to_date('X', 'yyyymmdd')) -
           trunc(to_date('X', 'yyyymmdd'), 'mm'))

或者

select first + rownum - 1 myday
  from (select trunc(to_date('X', 'yyyymmdd'), 'MM') first,
               trunc(last_day(to_date('X', 'yyyymmdd'))) last
          from dual)
connect by rownum <= last - first + 1

其中：字符串'X'表示某一个日期

19〉怎样知道今天是星期几

select to_char(sysdate,'day') from dual;

在获取之前可以设置日期语言,如:

ALTER SESSION SET NLS_DATE_LANGUAGE='AMERICAN';
还可以在函数中指定

select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = AMERICAN') from dual;
其它更多用法,可以参考to_char与to_date函数

20〉本月的天数

SELECT to_char(last_day(SYSDATE),'dd') days FROM dual

21〉今年的天数

select add_months(trunc(sysdate, 'year'), 12) - trunc(sysdate, 'year') /*下一年的第一天减去今年的第一天*/
from dual

22〉下个星期一的日期

SELECT Next_day(SYSDATE,'monday') FROM dual

23〉怎么样从数据库中获得毫秒
9i以上版本，有一个timestamp类型获得毫秒，如

select to_char(systimestamp ,'yyyy-mm-dd hh24:mi:ssxff') time1,
to_char(current_timestamp,'yyyy-mm-dd hh24:mi:ssxff') time2
from dual;

24〉检索某一年度的日历表：

select case
         when (new_yweek = min(new_yweek)
               over(partition by mon order by new_yweek)) then
          mon
         else
          null
       end as mon,
       new_yweek as yweek,
       row_number() over(partition by mon order by new_yweek) as mweek,
       sum(decode(wday, '1', mday, null)) as sunday,
       sum(decode(wday, '2', mday, null)) as monday,
       sum(decode(wday, '3', mday, null)) as tuesday,
       sum(decode(wday, '4', mday, null)) as wednesday,
       sum(decode(wday, '5', mday, null)) as thursday,
       sum(decode(wday, '6', mday, null)) as friday,
       sum(decode(wday, '7', mday, null)) as saturday,
       &year as year
  from (select to_date(&year || '0101', 'yyyymmdd') + rownum - 1 as everyday,
               to_char(to_date(&year || '0101', 'yyyymmdd') + rownum - 1,
                       'mm') as mon,
               to_char(to_date(&year || '0101', 'yyyymmdd') + rownum - 1,
                       'w') as mweek,
               to_char(to_date(&year || '0101', 'yyyymmdd') + rownum - 1,
                       'ww') as yweek,
               case
                 when (to_char(to_date(&year || '0101', 'yyyymmdd'), 'd') > '1') and
                      (to_char(to_date(&year || '0101', 'yyyymmdd') + rownum - 1,
                               'd') <
                      to_char(to_date(&year || '0101', 'yyyymmdd'), 'd')) then
                  to_char(to_char(to_date(&year || '0101', 'yyyymmdd') +
                                  rownum - 1,
                                  'ww') + 1,
                          'fm00')
                 else
                  to_char(to_date(&year || '0101', 'yyyymmdd') + rownum - 1,
                          'ww')
               end as new_yweek,
               to_char(to_date(&year || '0101', 'yyyymmdd') + rownum - 1,
                       'd') as wday,
               to_char(to_date(&year || '0101', 'yyyymmdd') + rownum - 1,
                       'dd') as mday
          from (select rownum r from dual connect by rownum <= 366)
         where rownum <=
               to_char(to_date(&year || '1231', 'yyyymmdd'), 'ddd'))
 group by mon, new_yweek