将UTC日期时间转换为本地日期时间的最佳方法是什么。它不像getutcdate（）和getdate（）差别那么简单，因为差异会根据日期而变化。
CLR集成对我来说也不是一种选择。
几个月前我提出的针对这个问题的解决方案是有一个夏令时表，存储了接下来100年左右的开始和结束夏令时，这个解决方案似乎不太优雅，但是转换是快速（简单的表查找）
答案 0 :(得分：27)
创建两个表，然后加入它们以将存储的GMT日期转换为本地时间：
TimeZones e.g.
--------- ----
TimeZoneId 19
Name Eastern (GMT -5)
Offset -5
创建夏令时表并使用尽可能多的信息填充它（当地法律一直在变化，因此无法预测未来数年的数据）
DaylightSavings
---------------
TimeZoneId 19
BeginDst 3/9/2008 2:00 AM
EndDst 11/2/2008 2:00 AM
像这样加入他们：
inner join TimeZones tz on x.TimeZoneId=tz.TimeZoneId
left join DaylightSavings ds on tz.TimeZoneId=ds.LocalTimeZone
and x.TheDateToConvert between ds.BeginDst and ds.EndDst
转换日期如下：
dateadd(hh, tz.Offset +
case when ds.LocalTimeZone is not null
then 1 else 0 end, TheDateToConvert)
答案 1 :(得分：15)
如果您在美国并且只对从UTC / GMT到固定时区（例如EDT）感兴趣，则此代码就足够了。我今天掀起了它，并认为这是正确的，但使用风险自负。
假设您的日期位于“日期”列中，则将计算列添加到表'myTable'。希望其他人觉得这很有用。
ALTER TABLE myTable ADD date_edt AS
dateadd(hh,
-- The schedule through 2006 in the United States was that DST began on the first Sunday in April
-- (April 2, 2006), and changed back to standard time on the last Sunday in October (October 29, 2006).
-- The time is adjusted at 02:00 local time.
CASE WHEN YEAR(date) <= 2006 THEN
CASE WHEN
date >= '4/' + CAST(abs(8-DATEPART(dw,'4/1/' + CAST(YEAR(date) as varchar)))%7 + 1 as varchar) + '/' + CAST(YEAR(date) as varchar) + ' 2:00'
AND
date < '10/' + CAST(32-DATEPART(dw,'10/31/' + CAST(YEAR(date) as varchar)) as varchar) + '/' + CAST(YEAR(date) as varchar) + ' 2:00'
THEN -4 ELSE -5 END
ELSE
-- By the Energy Policy Act of 2005, daylight saving time (DST) was extended in the United States in 2007.
-- DST starts on the second Sunday of March, which is three weeks earlier than in the past, and it ends on
-- the first Sunday of November, one week later than in years past. This change resulted in a new DST period
-- that is four weeks (five in years when March has five Sundays) longer than in previous years.[35] In 2008
-- daylight saving time ended at 02:00 on Sunday, November 2, and in 2009 it began at 02:00 on Sunday, March 8.[36]
CASE WHEN
date >= '3/' + CAST(abs(8-DATEPART(dw,'3/1/' + CAST(YEAR(date) as varchar)))%7 + 8 as varchar) + '/' + CAST(YEAR(date) as varchar) + ' 2:00'
AND
date <
'11/' + CAST(abs(8-DATEPART(dw,'11/1/' + CAST(YEAR(date) as varchar)))%7 + 1 as varchar) + '/' + CAST(YEAR(date) as varchar) + ' 2:00'
THEN -4 ELSE -5 END
END
,date)
答案 2 :(得分：7)
FOR READ-ONLY 使用此功能（受Bob Albright's incorrect solution启发）：
SELECT
date1,
dateadd(hh,
-- The schedule through 2006 in the United States was that DST began on the first Sunday in April
-- (April 2, 2006), and changed back to standard time on the last Sunday in October (October 29, 2006).
-- The time is adjusted at 02:00 local time (which, for edt, is 07:00 UTC at the start, and 06:00 GMT at the end).
CASE WHEN YEAR(date1) <= 2006 THEN
CASE WHEN
date1 >= '4/' + CAST((8-DATEPART(dw,'4/1/' + CAST(YEAR(date1) as varchar)))%7 + 1 as varchar) + '/' + CAST(YEAR(date1) as varchar) + ' 7:00'
AND
date1 < '10/' + CAST(32-DATEPART(dw,'10/31/' + CAST(YEAR(date1) as varchar)) as varchar) + '/' + CAST(YEAR(date1) as varchar) + ' 6:00'
THEN -4 ELSE -5 END
ELSE
-- By the Energy Policy Act of 2005, daylight saving time (DST) was extended in the United States in 2007.
-- DST starts on the second Sunday of March, which is three weeks earlier than in the past, and it ends on
-- the first Sunday of November, one week later than in years past. This change resulted in a new DST period
-- that is four weeks (five in years when March has five Sundays) longer than in previous years. In 2008
-- daylight saving time ended at 02:00 edt (06:00 UTC) on Sunday, November 2, and in 2009 it began at 02:00 edt (07:00 UTC) on Sunday, March 8
CASE WHEN
date1 >= '3/' + CAST((8-DATEPART(dw,'3/1/' + CAST(YEAR(date1) as varchar)))%7 + 8 as varchar) + '/' + CAST(YEAR(date1) as varchar) + ' 7:00'
AND
date1 < '11/' + CAST((8-DATEPART(dw,'11/1/' + CAST(YEAR(date1) as varchar)))%7 + 1 as varchar) + '/' + CAST(YEAR(date1) as varchar) + ' 6:00'
THEN -4 ELSE -5 END
END
, date1) as date1Edt
from MyTbl
我在尝试编辑Bob Albright's wrong answer后发布了此答案。我纠正了时间并删除了多余的abs（），但我的编辑被多次拒绝了。我尝试解释，但被解雇为一个菜鸟。他是解决这个问题的绝佳方法！它让我开始朝着正确的方向前进。当他只是需要一个小调整时，我讨厌创建这个单独的答案，但我试过了¯\ _（ツ）_ /¯
答案 3 :(得分：7)
一种考虑夏令时的简单通用解决方案。给定“YourDateHere”中的UTC日期：
--Use Minutes ("MI") here instead of hours because sometimes
-- the UTC offset may be half an hour (e.g. 9.5 hours).
SELECT DATEADD(MI,
DATEDIFF(MI, SYSUTCDATETIME(),SYSDATETIME()),
YourUtcDateHere)[LocalDateTime]
答案 4 :(得分：5)
如果这些问题中的任何一个对您有影响，则不应将本地时间存储在数据库中：
答案 5 :(得分：5)
在Eric Z Beard's answer中，以下SQL
inner join TimeZones tz on x.TimeZoneId=tz.TimeZoneId
left join DaylightSavings ds on tz.TimeZoneId=ds.LocalTimeZone
and x.TheDateToConvert between ds.BeginDst and ds.EndDst
可能更准确地说是：
inner join TimeZones tz on x.TimeZoneId=tz.TimeZoneId
left join DaylightSavings ds on tz.TimeZoneId=ds.LocalTimeZone
and x.TheDateToConvert >= ds.BeginDst and x.TheDateToConvert < ds.EndDst
（以上代码未经测试）
原因是sql“between”语句是包含的。在DST的后端，这将导致2AM时间未转换为1AM。当然，时间2AM的可能性很小，但可能会发生，并且会导致转换无效。
答案 6 :(得分：0)
维护一个TimeZone表，或者使用扩展存储过程（xp_cmdshell或COM组件，或您自己的）来shell，并要求操作系统执行此操作。如果你去xp路线，你可能想要缓存一天的偏移量。
答案 7 :(得分：0)
我喜欢提供的答案@Eric Z Beard。
但是，为了避免每次都进行加入，这是怎么回事？
TimeZoneOffsets
---------------
TimeZoneId 19
Begin 1/4/2008 2:00 AM
End 1/9/2008 2:00 AM
Offset -5
TimeZoneId 19
Begin 1/9/2008 2:00 AM
End 1/4/2009 2:00 AM
Offset -6
TimeZoneId 20 --Hong Kong for example - no DST
Begin 1/1/1900
End 31/12/9999
Offset +8
然后
Declare @offset INT = (Select IsNull(tz.Offset,0) from YourTable ds
join TimeZoneOffsets tz on tz.TimeZoneId=ds.LocalTimeZoneId
and x.TheDateToConvert >= ds.Begin and x.TheDateToConvert < ds.End)
终于成为了
dateadd(hh, @offset, TheDateToConvert)
答案 8 :(得分：0)
我已经阅读了很多关于这个问题的StackOverflow帖子，并发现了很多方法。一些“有点”可以。我还发现了我试图在我的脚本中使用的MS引用（https://msdn.microsoft.com/en-us/library/mt612795.aspx）。我已设法达到所需的结果但我不确定这是否会在2005版本上运行。无论哪种方式，我希望这会有所帮助。
CREATE FUNCTION dbo.GetPst()
RETURNS DATETIME
AS
BEGIN
RETURN SYSDATETIMEOFFSET() AT TIME ZONE 'Pacific Standard Time'
END
SELECT dbo.GetPst()
CREATE FUNCTION dbo.ConvertUtcToPst(@utcTime DATETIME)
RETURNS DATETIME
AS
BEGIN
RETURN DATEADD(HOUR, 0 - DATEDIFF(HOUR, CAST(SYSDATETIMEOFFSET() AT TIME ZONE 'Pacific Standard Time' AS DATETIME), SYSDATETIME()), @utcTime)
END
SELECT dbo.ConvertUtcToPst('2016-04-25 22:50:01.900')
答案 9 :(得分：0)
我正在使用这个，因为我的所有日期都是从现在开始的。
button.keyEquivalent = String(Character(UnicodeScalar(NSLeftArrowFunctionKey)!))
对于历史日期（或处理DST的未来变化，我猜测Bob Albright的解决方案将是最佳选择。
我对代码所做的修改是使用目标列：
DATEADD(HH,(DATEPART(HOUR, GETUTCDATE())-DATEPART(HOUR, GETDATE()))*-1, GETDATE())
到目前为止，这似乎有效，但我很高兴收到反馈。
答案 10 :(得分：0)
这是我用来制作时区表的代码。它有点幼稚，但通常都足够好。
假设：
这是SQL：
-- make a table (#dst) of years 1970-2101. Note that DST could change in the future and
-- everything was all custom and jacked before 1970 in the US.
declare @first_year varchar(4) = '1970'
declare @last_year varchar(4) = '2101'
-- make a table of all the years desired
if object_id('tempdb..#years') is not null drop table #years
;with cte as (
select cast(@first_year as int) as int_year
,@first_year as str_year
,cast(@first_year + '-01-01' as datetime) as start_of_year
union all
select int_year + 1
,cast(int_year + 1 as varchar(4))
,dateadd(year, 1, start_of_year)
from cte
where int_year + 1 <= @last_year
)
select *
into #years
from cte
option (maxrecursion 500);
-- make a staging table of all the important DST dates each year
if object_id('tempdb..#dst_stage') is not null drop table #dst_stage
select dst_date
,time_period
,int_year
,row_number() over (order by dst_date) as ordinal
into #dst_stage
from (
-- start of year
select y.start_of_year as dst_date
,'start of year' as time_period
,int_year
from #years y
union all
select dateadd(year, 1, y.start_of_year)
,'start of year' as time_period
,int_year
from #years y
where y.str_year = @last_year
-- start of dst
union all
select
case
when y.int_year >= 2007 then
-- second sunday in march
dateadd(day, ((7 - datepart(weekday, y.str_year + '-03-08')) + 1) % 7, y.str_year + '-03-08')
when y.int_year between 1987 and 2006 then
-- first sunday in april
dateadd(day, ((7 - datepart(weekday, y.str_year + '-04-01')) + 1) % 7, y.str_year + '-04-01')
when y.int_year = 1974 then
-- special case
cast('1974-01-06' as datetime)
when y.int_year = 1975 then
-- special case
cast('1975-02-23' as datetime)
else
-- last sunday in april
dateadd(day, ((7 - datepart(weekday, y.str_year + '-04-24')) + 1) % 7, y.str_year + '-04-24')
end
,'start of dst' as time_period
,int_year
from #years y
-- end of dst
union all
select
case
when y.int_year >= 2007 then
-- first sunday in november
dateadd(day, ((7 - datepart(weekday, y.str_year + '-11-01')) + 1) % 7, y.str_year + '-11-01')
else
-- last sunday in october
dateadd(day, ((7 - datepart(weekday, y.str_year + '-10-25')) + 1) % 7, y.str_year + '-10-25')
end
,'end of dst' as time_period
,int_year
from #years y
) y
order by 1
-- assemble a final table
if object_id('tempdb..#dst') is not null drop table #dst
select a.dst_date +
case
when a.time_period = 'start of dst' then ' 03:00'
when a.time_period = 'end of dst' then ' 02:00'
else ' 00:00'
end as start_date
,b.dst_date +
case
when b.time_period = 'start of dst' then ' 02:00'
when b.time_period = 'end of dst' then ' 01:00'
else ' 00:00'
end as end_date
,cast(case when a.time_period = 'start of dst' then 1 else 0 end as bit) as is_dst
,cast(0 as bit) as is_ambiguous
,cast(0 as bit) as is_invalid
into #dst
from #dst_stage a
join #dst_stage b on a.ordinal + 1 = b.ordinal
union all
select a.dst_date + ' 02:00' as start_date
,a.dst_date + ' 03:00' as end_date
,cast(1 as bit) as is_dst
,cast(0 as bit) as is_ambiguous
,cast(1 as bit) as is_invalid
from #dst_stage a
where a.time_period = 'start of dst'
union all
select a.dst_date + ' 01:00' as start_date
,a.dst_date + ' 02:00' as end_date
,cast(0 as bit) as is_dst
,cast(1 as bit) as is_ambiguous
,cast(0 as bit) as is_invalid
from #dst_stage a
where a.time_period = 'end of dst'
order by 1
-------------------------------------------------------------------------------
-- Test Eastern
select
the_date as eastern_local
,todatetimeoffset(the_date, case when b.is_dst = 1 then '-04:00' else '-05:00' end) as eastern_local_tz
,switchoffset(todatetimeoffset(the_date, case when b.is_dst = 1 then '-04:00' else '-05:00' end), '+00:00') as utc_tz
--,b.*
from (
select cast('2015-03-08' as datetime) as the_date
union all select cast('2015-03-08 02:30' as datetime) as the_date
union all select cast('2015-03-08 13:00' as datetime) as the_date
union all select cast('2015-11-01 01:30' as datetime) as the_date
union all select cast('2015-11-01 03:00' as datetime) as the_date
) a left join
#dst b on b.start_date <= a.the_date and a.the_date < b.end_date
答案 11 :(得分：0)
--Adapted Bob Albright and WillDeStijl suggestions for SQL server 2014
--
--In this instance I had no dates prior to 2006, therefore I simplified the case example
--I had to add the variables for the assignment to allow trimming the timestamp from my resultset
DECLARE @MARCH_DST as DATETIME
SET @MARCH_DST='3/' + CAST((8-DATEPART(dw,'3/1/' + CAST(YEAR(getdate()) as varchar)))%7 + 8 as varchar) + '/' + CAST(YEAR(getdate()) as varchar) + ' 7:00'
DECLARE @NOV_DST as DATETIME
SET @NOV_DST='11/' + CAST((8-DATEPART(dw,'11/1/' + CAST(YEAR(getdate()) as varchar)))%7 + 1 as varchar) + '/' + CAST(YEAR(getdate()) as varchar) + ' 6:00'
select cast(dateadd(HOUR,
-- By the Energy Policy Act of 2005, daylight saving time (DST) was extended in the United States in 2007.
-- DST starts on the second Sunday of March, which is three weeks earlier than in the past, and it ends on
-- the first Sunday of November, one week later than in years past. This change resulted in a new DST period
-- that is four weeks (five in years when March has five Sundays) longer than in previous years. In 2008
-- daylight saving time ended at 02:00 edt (06:00 UTC) on Sunday, November 2, and in 2009 it began at 02:00 edt (07:00 UTC) on Sunday, March 8
CASE WHEN
date1 >=@MARCH_DST
AND
date1< @NOV_DST
THEN -4 ELSE -5 END
, date1) as DATE) as date1_edited