我正在寻找一些SQL来确定当前周是否包含该月的第N天。
实施例。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。所以从星期六开始的一个月不会在星期五到星期五之前看到星期五到星期五，这个星期日到星期五开始，这个星期五将是第三个星期五。
不确定是否需要PL / SQL。
答案 0 :(得分：4)
所有现代SQL平台都有丰富的日期/时间函数来进行日期算术。但是当我看到基于它们的SQL时，特别是对于像你这样的要求，我的眼睛茫然。
我使用精心设计的日历表。关于使用它，有两件事我喜欢很多。
如果您尝试回答“当前一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会是什么样子？ （我的日历表使用ISO周数，而不是严格的日历周。下面有两个解决方法。）
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至2012-08-25）不包含2012年8月的第三个星期五。（它包含第4个星期五。）
根本没有改变我的表格，我可以用这个查询回答你的第一个问题。它在一个公用表表达式中包装了您对一周的定义。如果我不得不在制作中使用这样的东西，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。
第二种方法是定义你自己的week_number列来替换我的iso_week列。然后，您可以像上面的第一个一样表达您的查询。
PostgreSQL中日历表的DDL。 DDL是标准SQL;但我不确定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。
包含填充表格的功能。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
答案 1 :(得分：3)
您可以简单地生成包含每个月的第N天的周数的日期范围，例如每个月的第3个星期五，有这样的查询：
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;
答案 2 :(得分：0)
可能有更好的方法，并考虑到你没有任何类型的calendar表，如果第4个星期五在本周，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，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，仅使用day和N值的动态查询可以获得所需的结果。像
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'));
如果仔细看，子查询中有一个完整的日历。这是 -
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);