1.判斷某一天是周幾
select to_char(sysdate,'day') from dual;
select to_char(to_date('2007-11-20','yyyy-mm-dd'),'day') from dual;
2.求某月的天數
select to_char(last_day(sysdate),'dd') days from dual;
select to_char(last_day(to_date('200802','YYYYMM')),'dd') from dual;
3.求某年的天數
select add_months(trunc(sysdate,'year'), 12) - trunc(sysdate,'year') from dual;
select add_months(trunc(to_date('2008','YYYY'),'year'), 12) - trunc(to_date('2008','YYYY'),'year') from dual;
4.求下個星期一的日期
在獲取之前可以設置日期語言，如：
ALTER SESSION SET NLS_DATE_LANGUAGE='SIMPLIFIED CHINESE';
select next_day(sysdate,'星期一') from dual;
select next_day(sysdate,2) from dual; --後面的數字是從星期日開始算起，所以爲2
ALTER SESSION SET NLS_DATE_LANGUAGE='AMERICAN';
select next_day(sysdate,'monday') from dual;
5.確定某天是當年的第幾周
select to_char(sysdate,'fmww') from dual;
select to_char(to_date('20071126','YYYYMMDD'),'fmww') from dual;
6.確定某天是當月的第幾周
select to_char(sysdate,'WW') - to_char(trunc(sysdate,'MM'),'WW') + 1 from dual
select to_char(to_date('20071125','YYYYMMDD'),'WW') - to_char(trunc(to_date('20071125','YYYYMMDD'),'MM'),'WW') + 1 from dual
7.確定某天是當年的第幾天
select to_char(sysdate,'DDD') from dual
8.確定某天是當月的第幾天
select to_char(sysdate,'DD') from dual;
9.確定某天是一週的第幾天
select to_char(sysdate,'D') - 1 from dual; --Oracle定義週日爲一週的第一天，所以要減一
10.求兩個日期間的天數
select floor(sysdate - to_date('20071125','YYYYMMDD')) from dual;
11.求兩個日期間的月數
select floor(months_between(sysdate, to_date('20071031','YYYYMMDD'))) from dual;
12.計算某天的小時、分、秒
select day,
TRUNC(a*24) Hours,
TRUNC(a*24*60 - 60*TRUNC(a*24)) Minutes,
TRUNC(a*24*60*60 - 60*TRUNC(a*24*60)) Seconds
from ( select trunc(sysdate) day, sysdate - trunc(sysdate) a from dual);
按周按月：
select to_char(date,'ww'),count(id) from table group by to_char(date,'ww')
select to_char(date,'yyyymm'),count(id) from table group by to_char(date,'yyyymm')