我有一个星期数（例如 23），我想获取该周的星期一和星期日的日期。
我假设星期一是一周的第一天（例如，我的脚本中有 SET DATEFIRST 1）。
【问题讨论】：
标签： sql sql-server-2005 date
您可以尝试一些 dateadd 逻辑...
dateadd(week, 23, '2011-01-01')
dateadd(day, 7, dateadd(week, 23, '2011-01-01'))
更新：
select dateadd(day, 23, dateadd(week, 23, '2011-01-01')) , Datename(weekday,dateadd(day, 23, dateadd(week, 23, '2011-01-01')));
// RETURNS 7/4/2011, Monday
select Datename(weekday,dateadd(day, 23, dateadd(week, 23, '2011-01-01')));
// RETURNS Monday
示例来自：http://msdn.microsoft.com/en-us/library/ms186819.aspx
DECLARE @datetime2 datetime2 = '2007-01-01 13:10:10.1111111'
SELECT 'year', DATEADD(year,1,@datetime2)
UNION ALL
SELECT 'quarter',DATEADD(quarter,1,@datetime2)
UNION ALL
SELECT 'month',DATEADD(month,1,@datetime2)
UNION ALL
SELECT 'dayofyear',DATEADD(dayofyear,1,@datetime2)
UNION ALL
SELECT 'day',DATEADD(day,1,@datetime2)
UNION ALL
SELECT 'week',DATEADD(week,1,@datetime2)
UNION ALL
SELECT 'weekday',DATEADD(weekday,1,@datetime2)
UNION ALL
SELECT 'hour',DATEADD(hour,1,@datetime2)
UNION ALL
SELECT 'minute',DATEADD(minute,1,@datetime2)
UNION ALL
SELECT 'second',DATEADD(second,1,@datetime2)
UNION ALL
SELECT 'millisecond',DATEADD(millisecond,1,@datetime2)
UNION ALL
SELECT 'microsecond',DATEADD(microsecond,1,@datetime2)
UNION ALL
SELECT 'nanosecond',DATEADD(nanosecond,1,@datetime2);
/*
Year 2008-01-01 13:10:10.1111111
quarter 2007-04-01 13:10:10.1111111
month 2007-02-01 13:10:10.1111111
dayofyear 2007-01-02 13:10:10.1111111
day 2007-01-02 13:10:10.1111111
week 2007-01-08 13:10:10.1111111
weekday 2007-01-02 13:10:10.1111111
hour 2007-01-01 14:10:10.1111111
minute 2007-01-01 13:11:10.1111111
second 2007-01-01 13:10:11.1111111
millisecond 2007-01-01 13:10:10.1121111
microsecond 2007-01-01 13:10:10.1111121
nanosecond 2007-01-01 13:10:10.1111111
*/
【讨论】：
dateadd(week, ... 似乎只是增加了 7 天。所以在 2011 年使用这种方法，每周从星期六开始。
dateadd(day, 23, dateadd(week, 23, '2011-01-01')) 不知道应该怎么做。
Declare @StartDate datetime;
Set @StartDate = '20110101';
With StartOfWeek As
(
Select DateAdd(
week
, 23
, DateAdd(
d
, -(DatePart(dw, @StartDate) - 1)
, @StartDate
) ) As Sunday
)
Select Sunday, DateAdd(d,1,Sunday) As Monday
From StartOfWeek
【讨论】：
DECLARE @startweek1 datetime
SET DATEFIRST 1
--first monday of year
SELECT @startweek1 = DATEADD(day, 8-DATEPART(weekday, '2011-01-01'), '2011-01-01')
--day based
SELECT
DATEADD(day, 22 * 7, @startweek1) AS MondayWeek23,
DATEADD(day, 23 * 7 -1 , @startweek1) AS SundayWeek23
--week based
SELECT
DATEADD(week, 22, @startweek1) AS MondayWeek23,
DATEADD(day, -1, DATEADD(week, 23 , @startweek1)) AS SundayWeek23
编辑：
如果第 1 周不像 Andomar 所说的那样从第 1 天开始，则此解决方案有效
编辑 2：
根据Wikipedia：2008-12-29 是 ISO 2009 年第 1 周的第 1 天。
正如 Andomar 所说，week numbers vary
Cyberkiwi 提到此代码在 2007 年是错误的：它的错误频率远不止于此。这同样适用于他的代码，它与 2007 年相匹配，但其他代码同样错误。
【讨论】：
DATEADD(day, 2-DATEPART(weekday, '2007-01-01'), '2007-01-01')（即只需将 8 更改为 2）
Sorry for not being OCD enough to try 没有在公共论坛上提供经过良好测试的代码的糟糕借口，倾向于将其他人标记为OCD。我要求道歉
X - datepart(dw, ...)，这个方法不错。
注意： 任何以假设年份为 2011 年开始的答案都可以采用静态的第一个日期，即在下面的最后一个查询中将 @firstMon 替换为静态日期 '20101227 '。
SET DATEFIRST 1
declare @targetYear int
declare @targetWeek int
select @targetYear = 2011, @targetWeek = 23
declare @firstMon datetime
set @firstMon = dateadd(d,1-datepart(dw, right(@targetYear,4)+'0101'),right(@targetYear,4)+'0101')
select
MonOfTargetWeek = dateadd(week, @targetWeek-1, @firstMon),
SunOfTargetWeek = dateadd(week, @targetWeek-1, @firstMon+6)
以及真正的最终查询 - 当它在该周不存在时返回 NULL 的 Mon/Sun，例如partial-week-one 的 Mon 或 partial-week-53 的 Sun
;with tmp(Mon, Sun) as (
select
MonOfTargetWeek = dateadd(week, @targetWeek-1, @firstMon),
SunOfTargetWeek = dateadd(week, @targetWeek-1, @firstMon+6)
)
select
RealMonday = case when Year(Mon)=@targetYear then Mon end,
RealSunday = case when Year(Sun)=@targetYear then Sun end
from tmp
我已经把代码变成了一个函数。
CREATE function dbo.getMonSunForWeek(@targetYear int, @targetWeek int)
returns table as return
with pre(firstMon) as (
select dateadd(d,1-datepart(dw, right(@targetYear,4)+'0101'),right(@targetYear,4)+'0101'))
, tmp(Mon, Sun) as (
select
dateadd(week, @targetWeek-1, firstMon),
dateadd(week, @targetWeek-1, firstMon+6)
from pre
)
select
Mon, Sun,
RealMonday = case when Year(Mon)=@targetYear then Mon end,
RealSunday = case when Year(Sun)=@targetYear then Sun end
from tmp
GO
在下面我展示了从 1950 年到 2047 年的整个年和周 (1-53) 范围。在 每一个情况下，当星期一/星期日已确定时，使用DATEPART(week) 向后工作，SQL Server 同意函数中的星期编号。
set datefirst 1;
select
[Year] = years.number,
[Week] = weeks.number,
[Mon] = fun.realmonday,
[Sun] = fun.realsunday,
[WeekX] = isnull(datepart(week, fun.realmonday), datepart(week, fun.realsunday)),
[MonX] = fun.Mon,
[SunX] = fun.Sun
from master..spt_values years
inner join master..spt_values weeks on weeks.type='P' and weeks.number between 1 and 53
cross apply dbo.getMonSunForWeek(years.number, weeks.number) fun
where years.type='P' and years.number between 1950 and 2047
order by [year], [Week]
2005-2006 年转换前后的输出
when including prior/next year
Year Week Mon-of-week Sun-of-week datepart(week) Mon -and- Sun
2005 52 2005-12-19 2005-12-25 52 2005-12-19 2005-12-25
2005 53 2005-12-26 NULL 53 2005-12-26 2006-01-01
2006 1 NULL 2006-01-01 1 2005-12-26 2006-01-01
2006 2 2006-01-02 2006-01-08 2 2006-01-02 2006-01-08
【讨论】：
日历表使这种日期查询变得非常简单。日历表只是在加载时计算和存储相关的日历详细信息，而不是在运行时计算。根据应用程序，这可以大大加快速度。这种方式与 dbms 无关；它只是在 WHERE 子句中使用文字。
select cal_date from calendar
where iso_year = 2011
and iso_week = 23
and cal_dow in ('Mon', 'Sun');
另一种仅依赖于日期表的方式。
select cal_date from calendar
where extract(isoyear from cal_date) = 2011
and extract(week from cal_date) = 23
and (extract(isodow from cal_date) = 1 or
extract(isodow from cal_date) = 7);
EXTRACT() 是标准SQL，但我不确定isoyear、week、isodow 子字段的名称是不是标准SQL。
【讨论】：
我们可以使用 DATEFIRST 变量来设置一周的开始日期。默认情况下，一周从星期日 (7) 开始。为了从星期一开始，我们将其值设置为 1。
# Printing default value
Select @@DATEFIRST; -- This will give 7 value i.e. default value
# Changing first day of the week to Monday.
Declare @CurrentWeekNumber int
SET DATEFIRST 1
set @CurrentWeekNumber= (SELECT DATEPART(WEEK, GETDATE()))
select @CurrentWeekNumber
PS：对 DATEFIRST 的更改对当前会话有效，即它不会影响其他可能依赖于不同周开始日期的数据库查询。
【讨论】：