oracle周数计算[转补]

心已赠人 2022-08-04 04:14 209阅读 0赞

=========================================================================  
\--日期计算，算第n周的第一天及最后一天是几号。  by keynes 2005.04.29  
=========================================================================  
\-- ww的算法为每年1月1日为第一周开始，date+6为每一周结尾  
\-- 例如20090101为第一周的第一天，而第一周的最后一天为20090101+6=20090107  
\-- 公式 每周第一天  ：date + 周 \* 7 - 7  
\--      每周最后一天  ：date + 周 \* 7 - 1

\-- 如果以ww格式为主，第1、17周的起迄如下  
SQL>select to\_date('20090101','yyyymmdd') + 1\*7-7,to\_date('20090101','yyyymmdd') + 1\*7-1 from dual;

TO\_DATE('20090101','YYYYMMDD')      TO\_DATE('20090101','YYYYMMDD')  
2009-01-01                                                     2009-01-07

SQL>select to\_date('20090101','yyyymmdd') + 17\*7-7,to\_date('20090101','yyyymmdd') + 17\*7-1 from dual;

TO\_DATE('20090101','YYYYMMDD')       TO\_DATE('20090101','YYYYMMDD')  
          2009-04-23                                                      2009-04-29

\-- 验证如下  
SQL>select to\_char(to\_date('20090422','yyyymmdd'),'ww') as weekn,

to\_char(to\_date('20090423','yyyymmdd'),'ww') as week1,

to\_char(to\_date('20090429','yyyymmdd'),'ww') as week2,

to\_char(to\_date('20090430','yyyymmdd'),'ww') as weekn2 from dual;

WEEKN    WEEK1     WEEK2    WEEKN2  
16               17              17             18

\-- 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20090101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

SQL>select next\_day(to\_date('20090101','yyyymmdd'),'星期一')+ 1 \* 7 - 7 as first\_day,  
          next\_day(to\_date('20090101','yyyymmdd'),2)+ 1 \* 7 - 1 as last\_day from dual;

FIRST\_DAY      LAST\_DAY

--------------------------------------  
          2009-01-05         2009-01-11

SQL>select next\_day(to\_date('20090101','yyyymmdd'),'星期一')+ 17 \* 7 - 7 as first\_day,  
          next\_day(to\_date('20090101','yyyymmdd'),2)+ 1 7\* 7 - 1 as last\_day from dual;

FIRST\_DAY      LAST\_DAY

--------------------------------------  
          2009-04-27         2009-05-03

PS:NEXT\_DAY   的用法，两个参数第1个是date，第2个是varchar2，返回date

SQL>select   next\_day(sysdate,'星期一')   from   dual;

NEXT\_DAY(SYSDATE,'星期一')

-------------------     
         2009-11-09 15:20:33

第2个参数可以是数字1-7，分别表示周日到周六

SQL>   select   next\_day(sysdate,7)   FROM   DUAL;     
         NEXT\_DAY(SYSDATE,7)    
        -------------------     
         2009-11-07 15:19:12

或者更改设置：     
  SQL>   select   NEXT\_DAY   (sysdate,   'MONDAY')   FROM   DUAL;     
  select   NEXT\_DAY   (sysdate,   'MONDAY')   FROM   DUAL     
  ORA-01846:   周中的日无效    
     
  SQL>   alter   session   set   NLS\_DATE\_LANGUAGE   =   American;      
  Session   altered    
     
  SQL>   select   NEXT\_DAY   (sysdate,   'MONDAY')   FROM   DUAL;        
  NEXT\_DAY(SYSDATE,'MONDAY')    
  --------------------------    
  2005-9-26   10:50:25

其它:

\----查今天是 "本月" 的第几周  
SQL>SELECT TO\_CHAR(SYSDATE,'WW') - TO\_CHAR(TRUNC(SYSDATE,'MM'),'WW')  AS weekOfMon from dual;  
或  
SQL>SELECT TO\_CHAR(SYSDATE,'W') AS weekOfMon from dual;

WEEKOFMON

\--------------------------  
1

\----- 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;

TO\_CHAR(SYSDATE,'IW')

\--------------------------  
45

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.  
   
参考文件：  
Format Models：[http://download-west.oracle.com/docs/cd/B10501\_01/server.920/a96540/sql\_elements4a.htm\#34512][http_download-west.oracle.com_docs_cd_B10501_01_server.920_a96540_sql_elements4a.htm_34512]

[http_download-west.oracle.com_docs_cd_B10501_01_server.920_a96540_sql_elements4a.htm_34512]: http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96540/sql_elements4a.htm#34512