详细讲解Oracle数据库的“周数计算”

2008-03-18

eNet&Ciweek

2)iw的算法为星期一至星期日算一周，且每年的第一个星期一为第一周，

例如20050101为星期六，所以用iw的算法是前年的53周，而20050103之后才是第一周的开始。

公式 每周第一天 ：next_day(date) + 周 * 7 - 7

每周最后一天：next_day(date) + 周 * 7 - 1

如果以iw格式为主，第1、17周的起迄如下

127.0.0.1:asdb:WF>select next_day(to_date('20050101','yyyymmdd'),'MONDAY')+ 1 * 7 - 7 as first_day,next_day(to_date('20050101','yyyymmdd'),'MONDAY')+ 1 * 7 - 1 as last_day from dual;

FIRST_DAY LAST_DAY

03-JAN-05 09-JAN-05

Elapsed: 00:00:00.00

127.0.0.1:asdb:WF>

127.0.0.1:asdb:WF>select next_day(to_date('20050101','yyyymmdd'),'MONDAY')+ 17 * 7 - 7 as first_day,next_day(to_date('20050101','yyyymmdd'),'MONDAY')+ 17 * 7 - 1 as last_day from dual;

FIRST_DAY LAST_DAY

25-APR-05 01-MAY-05

Elapsed: 00:00:00.00

127.0.0.1:asdb:WF>

验证如下

127.0.0.1:asdb:WF>select to_char(to_date('20050424','yyyymmdd'),'iw') as weekn,to_char(to_date('20050425','yyyymmdd'),'iw') as week1,to_char(to_date('20050501','yyyymmdd'),'iw') as week2,to_char(to_date('20050502','yyyymmdd'),'iw') as weekn2 from dual;

WEEK WEEK WEEK WEEK

---- ---- ---- ----

16 17 17 18

Elapsed: 00:00:00.00

3)其它：

A、查今天是 "本月" 的第几周

SELECT TO_CHAR(SYSDATE,'WW') - TO_CHAR(TRUNC(SYSDATE,'MM'),'WW') + 1 AS "weekOfMon" from dual;

或

SELECT TO_CHAR(SYSDATE,'W') AS "weekOfMon" from dual;

B、查今天是 "今年" 的第几周

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

或

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

附注：

上文所提之iw及ww格式在doc内解释如下

IW = Week of year (1-52 or 1-53) based on the ISO standard

WW = Week of year (1-53) where week 1 starts on the first day of the year and continues to the seventh day of the year.

包括各种日期计算

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