SQL 来确定当前周是否是包含每月 N 个星期五的周答案

【问题标题】：SQL to Determine if Current Week is Week Containing N Friday of MonthSQL 来确定当前周是否是包含每月 N 个星期五的周
【发布时间】：2012-08-21 21:59:26
【问题描述】：

我正在寻找一些 SQL 来确定当前周是否是包含该月第 N 天的那一周。

示例。我想知道我是否在包含本月第三个星期五的那一周。或者每月的哪一周包含第三个星期五。周应定义为从星期日开始到星期六结束。因此，从星期六开始的月份在第 4 周之前不会是星期五，而从星期日到星期五开始的月份会在该月的第三周看到它的第三个星期五。

不确定是否需要 PL/SQL。

【问题讨论】：

你用mysql和oracle都标记了这个，你用的是哪一个？
所以我们可以选择支持两个数据库引擎中的哪一个？

标签： sql oracle plsql

【解决方案1】：

所有现代 SQL 平台都有丰富的日期/时间函数来进行日期运算。但是当我看到基于它们构建的 SQL 时，尤其是对于像你这样的需求，我的眼睛呆滞了。

我改用精心制作的日历表。很多使用它有两点我很喜欢。

相对不熟练的实习生可以很快学会正确查询。
通常可以看出查询显然是正确的。

如果您试图回答“当前周是否包含当月的第三个星期五？”，那么针对我的日历表的查询将如下所示。（我的日历表使用 ISO 周数，而不是严格的日历周。以下两种解决方法。）

select cal_date
from calendar
where year_of_date = 2012 
  and iso_week = (select iso_week
                  from calendar
                  where cal_date = current_date)
  and day_of_week = 'Fri'
  and day_of_week_ordinal = 3;

它不返回任何行；本周（2012-08-19 到 2012-08-25）不包含 2012 年 8 月的第三个星期五。（它包含第四个星期五。）

根本不改变我的表，我可以用这个查询回答你的第一个问题。它将您对一周的定义包装在一个公用表表达式中。如果我必须在生产中使用这样的东西，我可能会创建一个视图而不是 CTE。

with current_week as (
  select *
  from calendar
  where cal_date between (select max(cal_date) 
                          from calendar 
                          where day_of_week = 'Sun' 
                            and cal_date <= current_date) 
                     and (select min(cal_date) 
                          from calendar 
                          where day_of_week = 'Sat' 
                            and cal_date >= current_date)
)
select cal_date
from current_week
where day_of_week = 'Fri'
  and day_of_week_ordinal = 3;

同样，它不返回任何行；同样的原因。

第二种选择是定义您自己的 week_number 列来替换我的 iso_week 列。然后你可以像上面第一个一样表达你的查询。

PostgreSQL 中日历表的 DDL。 DDL 是标准 SQL；不过，我不确定 iso_year 和 iso_week 上的 CHECK 约束是否是标准 SQL。添加适合您环境的索引。

包括一个填充表格的函数。应该很容易移植到 Oracle。

create table calendar (
  cal_date date primary key,
  year_of_date integer not null 
    check (year_of_date = extract(year from cal_date)),
  month_of_year integer not null 
    check (month_of_year = extract(month from cal_date)),
  day_of_month integer not null 
    check (day_of_month = extract(day from cal_date)),
  day_of_week char(3) not null 
    check (day_of_week = 
    case when extract(dow from cal_date) = 0 then 'Sun'
         when extract(dow from cal_date) = 1 then 'Mon'
         when extract(dow from cal_date) = 2 then 'Tue'
         when extract(dow from cal_date) = 3 then 'Wed'
         when extract(dow from cal_date) = 4 then 'Thu'
         when extract(dow from cal_date) = 5 then 'Fri'
         when extract(dow from cal_date) = 6 then 'Sat'
    end),
  day_of_week_ordinal integer not null
    check (day_of_week_ordinal = 
      case
        when day_of_month >= 1 and day_of_month <= 7 then 1
        when day_of_month >= 8 and day_of_month <= 14 then 2
        when day_of_month >= 15 and day_of_month <= 21 then 3
        when day_of_month >= 22 and day_of_month <= 28 then 4
        else 5
      end),
  iso_year integer not null 
    check (iso_year = extract(isoyear from cal_date)),
  iso_week integer not null 
    check (iso_week = extract(week from cal_date))

);


CREATE OR REPLACE FUNCTION insert_range_into_calendar(from_date date, to_date date)
  RETURNS void AS
$BODY$

DECLARE
    this_date date := from_date;
BEGIN

    while (this_date <= to_date) LOOP
        INSERT INTO calendar (cal_date, year_of_date, month_of_year, day_of_month, day_of_week, day_of_week_ordinal, iso_year, iso_week)
        VALUES (this_date, extract(year from this_date), extract(month from this_date), extract(day from this_date),
        case when extract(dow from this_date) = 0 then 'Sun'
             when extract(dow from this_date) = 1 then 'Mon'
             when extract(dow from this_date) = 2 then 'Tue'
             when extract(dow from this_date) = 3 then 'Wed'
             when extract(dow from this_date) = 4 then 'Thu'
             when extract(dow from this_date) = 5 then 'Fri'
             when extract(dow from this_date) = 6 then 'Sat'
        end,
        case when extract(day from this_date) between 1 and 7 then 1
             when extract(day from this_date) between 8 and 14 then 2
             when extract(day from this_date) between 15 and 21 then 3
             when extract(day from this_date) between 22 and 28 then 4
             when extract(day from this_date) > 28 then 5
        end,
        cast(extract(isoyear from this_date) as integer),
        cast(extract(week from this_date) as integer));
        this_date = this_date + interval '1 day';
    end loop;       

END;
$BODY$
  LANGUAGE plpgsql

【讨论】：

干净整洁。您能否包含一个脚本来生成您精心制作的日历表？
是的，但它在 PostgreSQL 中。我会在几个小时后发布。

【解决方案2】：

您可以简单地生成包含每个月的第 N 天的星期的日期范围，例如每个月的第三个星期五，查询如下：

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;

【讨论】：

这仅适用于某些 NLS 设置（因为 to_char('DY') 将返回特定于语言环境的字符串，而 to_char('D') 将返回美国/德语的不同值，例如 -星期在美国从星期日开始，在德国从星期一开始）。
谢谢弗兰克，是的，它只需要根据 NLS 设置进行调整。

【解决方案3】：

可能有更好的方法可以做到这一点，并且考虑到您没有任何类型的 calendar 表，如果第四个星期五在当前周，则下面的查询将返回“Y”-

查询周开始 Sunday 并结束 Saturday

SELECT 'Y' FROM
  (
   SELECT max(to_date(month||' '||fri,'MON YYYY DD')) DT FROM (
        SELECT LPAD( MONTH, 20-(20-LENGTH(MONTH))/2 ) MONTH,Sun, Mon, Tue,
               Wed, Thu, Fri, Sat
        FROM (SELECT TO_CHAR(dt,'fmMonthfm YYYY') MONTH,TO_CHAR(dt+1,'iw') week,
                    MAX(DECODE(TO_CHAR(dt,'d'),'1',LPAD(TO_CHAR(dt,'fmdd'),2))) Sun,
                    MAX(DECODE(TO_CHAR(dt,'d'),'2',LPAD(TO_CHAR(dt,'fmdd'),2))) Mon,
                    MAX(DECODE(TO_CHAR(dt,'d'),'3',LPAD(TO_CHAR(dt,'fmdd'),2))) Tue,
                    MAX(DECODE(TO_CHAR(dt,'d'),'4',LPAD(TO_CHAR(dt,'fmdd'),2))) Wed,
                    MAX(DECODE(TO_CHAR(dt,'d'),'5',LPAD(TO_CHAR(dt,'fmdd'),2))) Thu,
                    MAX(DECODE(TO_CHAR(dt,'d'),'6',LPAD(TO_CHAR(dt,'fmdd'),2))) Fri,
                    MAX(DECODE(TO_CHAR(dt,'d'),'7',LPAD(TO_CHAR(dt,'fmdd'),2))) Sat
                    FROM ( SELECT TRUNC(SYSDATE,'y')-1+ROWNUM dt
        FROM all_objects
        WHERE ROWNUM <= ADD_MONTHS(TRUNC(SYSDATE,'y'),12) - TRUNC(SYSDATE,'y'))
        GROUP BY TO_CHAR(dt,'fmMonthfm YYYY'), TO_CHAR( dt+1, 'iw' ))
        ORDER BY TO_DATE( MONTH, 'Month YYYY' ), TO_NUMBER(week))
    where to_char(to_date(month,'MON YYYY'),'MON YYYY') = to_char(sysdate,'MON YYYY')
      and fri is not null
      and rownum <= 4) a
where a.dt BETWEEN sysdate+(8 - to_char(sysdate,'d'))-7 
      AND sysdate+(7 - to_char(sysdate,'d'));

要检查第 N 天 - 只需替换 rownum <= N 并将 and fri is not null 子句更改为 and <your_day> is not null，并将 SELECT to_date(month||' '||fri,'MON YYYY DD') DT FROM .. 更改为 SELECT to_date(month||' '||<your_day>,'MON YYYY DD') DT FROM ..。

因此，仅包含 day 和 N 值的动态查询可以获得所需的结果。喜欢

SELECT 'Y' FROM
      (
       SELECT max(to_date(month||' '||:day,'MON YYYY DD')) DT FROM (
            SELECT LPAD( MONTH, 20-(20-LENGTH(MONTH))/2 ) MONTH,Sun, Mon, Tue,
                   Wed, Thu, Fri, Sat
            FROM (SELECT TO_CHAR(dt,'fmMonthfm YYYY') MONTH,TO_CHAR(dt+1,'iw') week,
                        MAX(DECODE(TO_CHAR(dt,'d'),'1',LPAD(TO_CHAR(dt,'fmdd'),2))) Sun,
                        MAX(DECODE(TO_CHAR(dt,'d'),'2',LPAD(TO_CHAR(dt,'fmdd'),2))) Mon,
                        MAX(DECODE(TO_CHAR(dt,'d'),'3',LPAD(TO_CHAR(dt,'fmdd'),2))) Tue,
                        MAX(DECODE(TO_CHAR(dt,'d'),'4',LPAD(TO_CHAR(dt,'fmdd'),2))) Wed,
                        MAX(DECODE(TO_CHAR(dt,'d'),'5',LPAD(TO_CHAR(dt,'fmdd'),2))) Thu,
                        MAX(DECODE(TO_CHAR(dt,'d'),'6',LPAD(TO_CHAR(dt,'fmdd'),2))) Fri,
                        MAX(DECODE(TO_CHAR(dt,'d'),'7',LPAD(TO_CHAR(dt,'fmdd'),2))) Sat
                        FROM ( SELECT TRUNC(SYSDATE,'y')-1+ROWNUM dt
            FROM all_objects
            WHERE ROWNUM <= ADD_MONTHS(TRUNC(SYSDATE,'y'),12) - TRUNC(SYSDATE,'y'))
            GROUP BY TO_CHAR(dt,'fmMonthfm YYYY'), TO_CHAR( dt+1, 'iw' ))
            ORDER BY TO_DATE( MONTH, 'Month YYYY' ), TO_NUMBER(week))
        where to_char(to_date(month,'MON YYYY'),'MON YYYY') = to_char(sysdate,'MON YYYY')
          and :day is not null
          and rownum <= :num) a
    where a.dt BETWEEN sysdate+(8 - to_char(sysdate,'d'))-7 
          AND sysdate+(7 - to_char(sysdate,'d'));

如果您仔细看，子查询中有一个完整的日历。哪个是-

SELECT LPAD( MONTH, 20-(20-LENGTH(MONTH))/2 ) MONTH,Sun, Mon, Tue,
               Wed, Thu, Fri, Sat
        FROM (SELECT TO_CHAR(dt,'fmMonthfm YYYY') MONTH,TO_CHAR(dt+1,'iw') week,
                    MAX(DECODE(TO_CHAR(dt,'d'),'1',LPAD(TO_CHAR(dt,'fmdd'),2))) Sun,
                    MAX(DECODE(TO_CHAR(dt,'d'),'2',LPAD(TO_CHAR(dt,'fmdd'),2))) Mon,
                    MAX(DECODE(TO_CHAR(dt,'d'),'3',LPAD(TO_CHAR(dt,'fmdd'),2))) Tue,
                    MAX(DECODE(TO_CHAR(dt,'d'),'4',LPAD(TO_CHAR(dt,'fmdd'),2))) Wed,
                    MAX(DECODE(TO_CHAR(dt,'d'),'5',LPAD(TO_CHAR(dt,'fmdd'),2))) Thu,
                    MAX(DECODE(TO_CHAR(dt,'d'),'6',LPAD(TO_CHAR(dt,'fmdd'),2))) Fri,
                    MAX(DECODE(TO_CHAR(dt,'d'),'7',LPAD(TO_CHAR(dt,'fmdd'),2))) Sat
                    FROM ( SELECT TRUNC(SYSDATE,'y')-1+ROWNUM dt
        FROM all_objects
        WHERE ROWNUM <= ADD_MONTHS(TRUNC(SYSDATE,'y'),12) - TRUNC(SYSDATE,'y'))
        GROUP BY TO_CHAR(dt,'fmMonthfm YYYY'), TO_CHAR( dt+1, 'iw' ))
        ORDER BY TO_DATE( MONTH, 'Month YYYY' ), TO_NUMBER(week);

【讨论】：