我需要在SQL服务器中创建一个函数，该函数返回夏令时开始日期时间和夏令时结束日期时间。
我在网上看到了一些例子，但他们都使用了3月的第1个日期和11月的第1个日期，这在技术上并不正确。
夏令时从3月的第2个星期日凌晨2点开始，到11月的第一个星期日凌晨2点结束。
我从下面的代码开始，但我确定它错了。任何帮助表示赞赏！ ：）
DECLARE @DSTSTART DATETIME
SELECT @DSTSTART = CASE WHEN
DATEPART(MONTH, SYSDATETIME()) = 3
AND DATEPART(weekday, SYSDATETIME()) = 1
AND DATEDIFF(week,dateadd(week, datediff(week, 0, dateadd(month, datediff(month, 0, SYSDATETIME()), 0)), 0), SYSDATETIME() - 1) = 2
AND DATEPART(HOUR, SYSDATETIME()) = 2
THEN SYSDATETIME()
END
RETURN (@DSTSTART)
END
GO
答案 0 :(得分：16)
不要忘记夏令时时间表会根据国家/地区而变化，并且多年来也会发生变化：例如，当前的美国系统于2007年生效。
假设你想要美国当前的系统，这是任何一年的答案的一种形式。
SET DATEFIRST 7
DECLARE @year INT = 2013
DECLARE
@StartOfMarch DATETIME ,
@StartOfNovember DATETIME ,
@DstStart DATETIME ,
@DstEnd DATETIME
SET @StartOfMarch = DATEADD(MONTH, 2, DATEADD(YEAR, @year - 1900, 0))
SET @StartOfNovember = DATEADD(MONTH, 10, DATEADD(YEAR, @year - 1900, 0));
SET @DstStart = DATEADD(HOUR, 2,
DATEADD(day,
( ( 15 - DATEPART(dw, @StartOfMarch) ) % 7 )
+ 7, @StartOfMarch))
SET @DstEnd = DATEADD(HOUR, 2,
DATEADD(day,
( ( 8 - DATEPART(dw, @StartOfNovember) ) % 7 ),
@StartOfNovember))
SELECT
@DstStart AS DstStartInUS ,
@DstEnd AS DstEndInUS
或作为函数，但您必须知道DateFirst设置为7，否则数学将关闭。
CREATE FUNCTION GetDstStart ( @Year AS INT )
RETURNS DATETIME
AS
BEGIN
DECLARE
@StartOfMarch DATETIME ,
@DstStart DATETIME
SET @StartOfMarch = DATEADD(MONTH, 2,
DATEADD(YEAR, @year - 1900, 0))
SET @DstStart = DATEADD(HOUR, 2,
DATEADD(day,
( ( 15 - DATEPART(dw,
@StartOfMarch) )
% 7 ) + 7, @StartOfMarch))
RETURN @DstStart
END
GO;
CREATE FUNCTION GetDstEnd ( @Year AS INT )
RETURNS DATETIME
AS
BEGIN
DECLARE
@StartOfNovember DATETIME ,
@DstEnd DATETIME
SET @StartOfNovember = DATEADD(MONTH, 10,
DATEADD(YEAR, @year - 1900, 0))
SET @DstEnd = DATEADD(HOUR, 2,
DATEADD(day,
( ( 8 - DATEPART(dw,
@StartOfNovember) )
% 7 ), @StartOfNovember))
RETURN @DstEnd
END
答案 1 :(得分：4)
就我个人而言，我认为11月的第一个星期日比找到3月的第二个星期日更容易。幸运的是，如果你找到一个，你可以找到另一个，因为它们之间总是有238天。所以这里有一个方便的功能来找到Dst的结尾：
create function GetDstEnd (
@Year int
)
returns datetime
as
begin
declare @DstEnd datetime;
;with FirstWeekOfNovember
as (
select top(7)
cast(@Year as char(4))
+ '-11-0'
+ cast(row_number() over(order by object_id) as char(1))
+ ' 02:00:00'
'DST_Stops'
from sys.columns
)
select @DstEnd = DST_Stops
from FirstWeekOfNovember
where datepart(weekday,DST_Stops) = 1
return @DstEnd;
end;
现在Dst的开始是相同的功能，仅在238天之前。
create function GetDstStart (
@Year int
)
returns datetime
as
begin;
declare @DstStart datetime;
;with FirstWeekOfNovember
as (
select top(7)
cast(@Year as char(4))
+ '-11-0'
+ cast(row_number() over(order by object_id) as char(1))
+ ' 02:00:00'
'DST_Stops'
from sys.columns
)
select @DstStart = dateadd(day,-238,DST_Stops)
from FirstWeekOfNovember
where datepart(weekday,DST_Stops) = 1
return @DstStart;
end;
go
答案 2 :(得分：3)
SQL Server 2016版将解决此问题once and for all。对于早期版本，CLR解决方案可能最简单。或者对于特定的DST规则（仅限于美国），T-SQL函数可以相对简单。
但是，我认为通用的T-SQL解决方案可能是可行的。只要xp_regread有效，请尝试以下方法：
CREATE TABLE #tztable (Value varchar(50), Data binary(56));
DECLARE @tzname varchar(150) = 'SYSTEM\CurrentControlSet\Control\TimeZoneInformation'
EXEC master.dbo.xp_regread 'HKEY_LOCAL_MACHINE', @tzname, 'TimeZoneKeyName', @tzname OUT;
SELECT @tzname = 'SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones\' + @tzname
INSERT INTO #tztable
EXEC master.dbo.xp_regread 'HKEY_LOCAL_MACHINE', @tzname, 'TZI';
SELECT -- See http://msdn.microsoft.com/ms725481
CAST(CAST(REVERSE(SUBSTRING(Data, 1, 4)) AS binary(4)) AS int) AS BiasMinutes, -- UTC = local + bias: > 0 in US, < 0 in Europe!
CAST(CAST(REVERSE(SUBSTRING(Data, 5, 4)) AS binary(4)) AS int) AS ExtraBias_Std, -- 0 for most timezones
CAST(CAST(REVERSE(SUBSTRING(Data, 9, 4)) AS binary(4)) AS int) AS ExtraBias_DST, -- -60 for most timezones: DST makes UTC 1 hour earlier
-- When DST ends:
CAST(CAST(REVERSE(SUBSTRING(Data, 13, 2)) AS binary(2)) AS smallint) AS StdYear, -- 0 = yearly (else once)
CAST(CAST(REVERSE(SUBSTRING(Data, 15, 2)) AS binary(2)) AS smallint) AS StdMonth, -- 0 = no DST
CAST(CAST(REVERSE(SUBSTRING(Data, 17, 2)) AS binary(2)) AS smallint) AS StdDayOfWeek, -- 0 = Sunday to 6 = Saturday
CAST(CAST(REVERSE(SUBSTRING(Data, 19, 2)) AS binary(2)) AS smallint) AS StdWeek, -- 1 to 4, or 5 = last <DayOfWeek> of <Month>
CAST(CAST(REVERSE(SUBSTRING(Data, 21, 2)) AS binary(2)) AS smallint) AS StdHour, -- Local time
CAST(CAST(REVERSE(SUBSTRING(Data, 23, 2)) AS binary(2)) AS smallint) AS StdMinute,
CAST(CAST(REVERSE(SUBSTRING(Data, 25, 2)) AS binary(2)) AS smallint) AS StdSecond,
CAST(CAST(REVERSE(SUBSTRING(Data, 27, 2)) AS binary(2)) AS smallint) AS StdMillisec,
-- When DST starts:
CAST(CAST(REVERSE(SUBSTRING(Data, 29, 2)) AS binary(2)) AS smallint) AS DSTYear, -- See above
CAST(CAST(REVERSE(SUBSTRING(Data, 31, 2)) AS binary(2)) AS smallint) AS DSTMonth,
CAST(CAST(REVERSE(SUBSTRING(Data, 33, 2)) AS binary(2)) AS smallint) AS DSTDayOfWeek,
CAST(CAST(REVERSE(SUBSTRING(Data, 35, 2)) AS binary(2)) AS smallint) AS DSTWeek,
CAST(CAST(REVERSE(SUBSTRING(Data, 37, 2)) AS binary(2)) AS smallint) AS DSTHour,
CAST(CAST(REVERSE(SUBSTRING(Data, 39, 2)) AS binary(2)) AS smallint) AS DSTMinute,
CAST(CAST(REVERSE(SUBSTRING(Data, 41, 2)) AS binary(2)) AS smallint) AS DSTSecond,
CAST(CAST(REVERSE(SUBSTRING(Data, 43, 2)) AS binary(2)) AS smallint) AS DSTMillisec
FROM #tztable;
DROP TABLE #tztable
（复杂）T-SQL函数可以使用this data来确定当前DST规则中所有日期的确切偏移量。
答案 3 :(得分：0)
我对在线找到的将UTC转换为当地时间的任何解决方案都不满意，因此我想到了此功能。 Have a look at my SO answer here
其中存在一些逻辑，可以根据DST使用的标准日期范围来计算夏令时是否有效（3月的第二个星期日，凌晨2点，时钟向前移动； 11月的第一个星期日，恢复为标准时间）