将历史日期从UTC转换为本地时间

Question

I have an sql table with data like this:

| theDate (datetime)  | theValue (int) |
----------------------------------------
| 2010-05-17 02:21:10 |              5 |
| 2009-03-12 04:11:35 |             23 |
| 2010-02-19 18:16:53 |             52 |
| 2008-07-07 22:54:11 |             30 |

这些日期存储在 datetime 列中，格式为 UTC，我该如何将它们转换为当地时间（挪威）？请记住由于冬令/夏令时的原因，UTC 偏移并非全年相同。

更新：我正在使用 Microsoft SQL Server 2005，并且需要从 SQL 中进行此操作，因为数据稍后将显示在报告中。

- Espo

Answer 1

这个语句将适用于您列出的表。使用这种逻辑，您可以将其应用于任何日期字段。

    SELECT CASE
         WHEN [theDate] BETWEEN 
         Convert(DATETIME, Convert(VARCHAR(4), Year([theDate])) + '-03-' + Convert(VARCHAR(2), (31 - (5 * Year([theDate])/4 + 4) % 7)) + ' 02:00:00', 20)
         AND
         Convert(DATETIME, Convert(VARCHAR(4), Year([theDate])) + '-10-' + Convert(VARCHAR(2), (31 - (5 * Year([theDate])/4 + 1) % 7)) + ' 03:00:00', 20)
         THEN Dateadd(hh, 2, [theDate])
         ELSE Dateadd(hh, 1, [theDate])
       END AS [theDate],
       [theValue]
FROM   [YOURTABLE] 

- Kenneth

---

这如何考虑到UTC偏移量不是一整年都相同的呢？ - Espo

太棒了！但是你能描述一下逻辑吗？我不太明白这是怎么工作的。（魔法！） - Tobb

Answer 2

编写CLR函数，将SqlDateTime从UTC转换为CLR本地时间，类似于以下内容：

[Microsoft.SqlServer.Server.SqlFunction]
public static SqlDateTime ToLocalTime(SqlDateTime dt)
{
    try
    {
         return TimeZone.CurrentTimeZone.ToLocalTime(dt.Value);
    }
    catch
    {
        return SqlDateTime.Null;
    }
}

- Slawomir Brys

Answer 3

这是我的函数，用于从本地时间返回冬令时

基于每年三月的最后一个星期日的2:00和十月的最后一个星期日的3:00的时间更改

use your_DB
go
CREATE function [dbo].[ConvertToLocalWinterTime](@instime datetime)
returns datetime
as
begin
declare @localtm datetime = @instime
declare @localwintertm datetime
declare @lastmarchsunday datetime
declare @lastoctobersunday datetime
declare @tmpmd datetime = '03.31.' + convert(char(4),year(@localtm))
declare @tmpod datetime = '10.31.' + convert(char(4),year(@localtm))

    --- last sunday in march
    declare  @DOFWEEKM int = datepart (weekday,@tmpmd-1) 
    if @DOFWEEKM <7
    begin
    set @lastmarchsunday = @tmpmd - @DOFWEEKM 
    end
    else 
    begin
    set @lastmarchsunday = @tmpmd 
    end
    ----last sunday in October
    declare  @DOFWEEKO int = datepart (weekday,@tmpod-1) 
    if @DOFWEEKO <7
    begin
    set @lastoctobersunday = @tmpod - @DOFWEEKO
    end
    else 
    begin
    set @lastoctobersunday = @tmpod
    end
    -------------------------------
    if (@localtm > dateadd(hh,2,@lastmarchsunday)) and (@localtm < dateadd(hh,3,@lastoctobersunday))
    begin
    set @localwintertm =  dateadd(hh,-1, @localtm)
    end
    else 
    begin
    set @localwintertm = @localtm
    end

return @localwintertm
end

- Luftar

Answer 4

如果你能使用PHP...

$dateFormat = 'r';
$tz         = 'Australia/Perth';
function convertDate($epochDate) {
  global $dateFormat, $tz;
  $tzOld = getenv("TZ");
  putenv("TZ=$tz");
  $ret = date($dateFormat, ($epochDate*1));
  putenv("TZ" . ($tzOld ? "=$tzOld" : ""));
  return $ret;
}

- Delan Azabani