用于确定当前周是否为包含N个星期五的周的SQL

Question

我正在寻找一些SQL来确定当前周是否包含该月的第N天.

例.我想知道我是否在包含本月第三个星期五的那个星期.或者该月的哪个星期包含第三个星期五.周应定义为从星期日开始到星期六结束.因此,从星期六开始的一个月不会在星期五到星期五之前看到,从星期日到星期五开始的一个月,将会在本月的第3周看到它是第3个星期五.

不确定是否需要PL/SQL.

Answer 1

您可以简单地生成包含每月第 N 天的周的日期范围，例如每月的第三个星期五，使用如下查询：

select d - day_of_week AS sunday
      ,d + (7 - day_of_week) AS saturday
from   (select trunc(sysdate,'YY')+rownum-1 AS d
              ,to_number(to_char(trunc(sysdate,'YY')+rownum-1,'D'))
               AS day_of_week
        from dual connect by level <= 366)
where  to_char(d,'W') = 3
and    to_char(d,'DY') = 'FRI';

SUNDAY      SATURDAY
==========  ==========
14/01/2012  21/01/2012
11/02/2012  18/02/2012
10/03/2012  17/03/2012
14/04/2012  21/04/2012
12/05/2012  19/05/2012
09/06/2012  16/06/2012
14/07/2012  21/07/2012
11/08/2012  18/08/2012
15/09/2012  22/09/2012
13/10/2012  20/10/2012
10/11/2012  17/11/2012
15/12/2012  22/12/2012

编辑：您可以创建一个简单的函数来检查单个日期，例如：

CREATE FUNCTION date_in_week_of_nth_day
   (in_date IN DATE
   ,in_week IN NUMBER
   ,in_day  IN VARCHAR2
   ) RETURN CHAR IS
  ret CHAR(1);
BEGIN
  select 'Y' into ret
  from   (select trunc(in_date,'MM')+rownum-1 AS d
                ,to_number(to_char(trunc(in_date,'MM')+rownum-1,'D'))
                 AS day_of_week
          from dual connect by level <= 31)
  where  to_char(d,'W') = in_week
  and    to_char(d,'DY') = in_day
  and    :in_date between (d - day_of_week) and (d + (7 - day_of_week));
  RETURN ret;
EXCEPTION
  WHEN NO_DATA_FOUND THEN
    RETURN 'N';
END;