如何将datetime转换为datetimeoffset？

Question

如何将SQL Server datetime值转换为datetimeoffset值？

---

例如,现有表包含datetime全部处于"本地"服务器时间的值.

SELECT TOP 5 ChangeDate FROM AuditLog

ChangeDate
=========================
2013-07-25 04:00:03.060
2013-07-24 04:00:03.073
2013-07-23 04:00:03.273
2013-07-20 04:00:02.870
2013-07-19 04:00:03.780

我的服务器(恰好)(现在,今天)比UTC晚了四个小时(现在,在美国东部时区,夏令时处于活动状态):

SELECT SYSDATETIMEOFFSET()

2013-07-25 14:42:41.6450840 -04:00

我想将存储的datetime值转换为datetimeoffset值; 使用服务器的当前时区偏移信息.

我想要的价值观是:

ChangeDate               ChangeDateOffset
=======================  ==================================
2013-07-25 04:00:03.060  2013-07-25 04:00:03.0600000 -04:00
2013-07-24 04:00:03.073  2013-07-24 04:00:03.0730000 -04:00
2013-07-23 04:00:03.273  2013-07-23 04:00:03.2730000 -04:00
2013-07-20 04:00:02.870  2013-07-20 04:00:02.8700000 -04:00
2013-07-19 04:00:03.780  2013-07-19 04:00:03.7800000 -04:00

你可以看到理想的特征:

2013-07-19 04:00:03.7800000 -04:00
--------------------------- ------
           |                    |
   a "local" datetime        the offset from UTC

但相反,实际值是:

SELECT TOP 5
   ChangeDate,
   CAST(ChangeDate AS datetimeoffset) AS ChangeDateOffset
FROM AuditLog

ChangeDate               ChangeDateOffset
=======================  ==================================
2013-07-25 04:00:03.060  2013-07-25 04:00:03.0600000 +00:00
2013-07-24 04:00:03.073  2013-07-24 04:00:03.0730000 +00:00
2013-07-23 04:00:03.273  2013-07-23 04:00:03.2730000 +00:00
2013-07-20 04:00:02.870  2013-07-20 04:00:02.8700000 +00:00
2013-07-19 04:00:03.780  2013-07-19 04:00:03.7800000 +00:00

具有无效特征:

2013-07-19 04:00:03.7800000 +00:00
--------------------------- ------
                              ^
                              |
                             No offset from UTC present

所以我随机尝试其他事情:

SELECT TOP 5
    ChangeDate, 
    CAST(ChangeDate AS datetimeoffset) AS ChangeDateOffset,
    DATEADD(minute, DATEDIFF(minute, GETDATE(), GETUTCDATE()), ChangeDate) AS ChangeDateUTC,
    CAST(DATEADD(minute, DATEDIFF(minute, GETDATE(), GETUTCDATE()), ChangeDate) AS datetimeoffset) AS ChangeDateUTCOffset,
    SWITCHOFFSET(CAST(ChangeDate AS datetimeoffset), DATEDIFF(minute, GETUTCDATE(), GETDATE())) AS ChangeDateSwitchedOffset
FROM AuditLog
ORDER BY ChangeDate DESC

结果如下:

ChangeDate               ChangeDateOffset                    ChangeDateUTC            ChangeDateUTCOffset                 ChangeDateSwitchedOffset
=======================  ==================================  =======================  ==================================  ==================================
2013-07-25 04:00:03.060  2013-07-25 04:00:03.0600000 +00:00  2013-07-25 08:00:03.060  2013-07-25 08:00:03.0600000 +00:00  2013-07-25 00:00:03.0600000 -04:00
2013-07-24 04:00:03.073  2013-07-24 04:00:03.0730000 +00:00  2013-07-24 08:00:03.073  2013-07-24 08:00:03.0730000 +00:00  2013-07-24 00:00:03.0730000 -04:00
2013-07-23 04:00:03.273  2013-07-23 04:00:03.2730000 +00:00  2013-07-23 08:00:03.273  2013-07-23 08:00:03.2730000 +00:00  2013-07-23 00:00:03.2730000 -04:00
2013-07-20 04:00:02.870  2013-07-20 04:00:02.8700000 +00:00  2013-07-20 08:00:02.870  2013-07-20 08:00:02.8700000 +00:00  2013-07-20 00:00:02.8700000 -04:00
2013-07-19 04:00:03.780  2013-07-19 04:00:03.7800000 +00:00  2013-07-19 08:00:03.780  2013-07-19 08:00:03.7800000 +00:00  2013-07-19 00:00:03.7800000 -04:00
                         ----------------------------------                           ----------------------------------  ----------------------------------
                                              No UTC offset                           Time in UTC          No UTC offset  Time all wrong

它们都没有返回所需的值.

任何人都可以建议回归我直觉所需的东西吗？

Answer 1

我想到了.诀窍是有一个内置的SQL Server函数ToDateTimeOffset,它将任意偏移信息附加到任何提供的datetime.

例如,相同的查询:

SELECT ToDateTimeOffset('2013-07-25 15:35:27', -240)     --  -240 minutes
SELECT ToDateTimeOffset('2013-07-25 15:35:27', '-04:00') --  -4 hours

两者都回归:

2013-07-25 15:35:27.0000000 -04:00

注意:offset参数ToDateTimeOffset可以是:

• 一个integer,代表几分钟
• a string,代表小时和分钟({+|-}TZH:THM格式)

我们需要服务器的当前UTC偏移量

接下来我们需要服务器与UTC的当前偏移量.我有两种方法可以让SQL Server返回integerUTC的分钟数:

DATEPART(TZOFFSET, SYSDATETIMEOFFSET()) 
DATEDIFF(minute, GETUTCDATE(), GETDATE())

都归来了

-240

将其插入TODATETIMEOFFSET功能:

SELECT ToDateTimeOffset(
      '2013-07-25 15:35:27',
      DATEPART(TZOFFSET, SYSDATETIMEOFFSET()) --e.g. -240
)

返回datetimeoffset我想要的值:

2013-07-25 15:35:27.0000000 -04:00

完全放在一起

现在我们可以有更好的功能将datetime转换为datetimeoffset:

CREATE FUNCTION dbo.ToDateTimeOffset(@value datetime2)
    RETURNS datetimeoffset AS
BEGIN
/*
    Converts a date/time without any timezone offset into a datetimeoffset value, 
    using the server's current offset from UTC. 

    For this we use the builtin ToDateTimeOffset function; 
    which attaches timezone offset information with a datetimeoffset value.

    The trick is to use DATEDIFF(minutes) between local server time and UTC 
    to get the offset parameter.

    For example:
        DATEPART(TZOFFSET, SYSDATETIMEOFFSET())
    returns the integer
        -240

    for people in EDT (Eastern Daylight Time), which is 4 hours (240 minutes) behind UTC.
    Pass that value to the SQL Server function:
        TODATETIMEOFFSET(@value, -240)
*/

    RETURN TODATETIMEOFFSET(@value, DATEPART(TZOFFSET, SYSDATETIMEOFFSET()))
END;

样品用法

SELECT TOP 5
    ChangeDate, 
    dbo.ToDateTimeOffset(ChangeDate) AS ChangeDateOffset
FROM AuditLog

返回所需的:

ChangeDate               ChangeDateOffset
=======================  ==================================
2013-07-25 04:00:03.060  2013-07-25 04:00:03.0600000 -04:00
2013-07-24 04:00:03.073  2013-07-24 04:00:03.0730000 -04:00
2013-07-23 04:00:03.273  2013-07-23 04:00:03.2730000 -04:00
2013-07-20 04:00:02.870  2013-07-20 04:00:02.8700000 -04:00
2013-07-19 04:00:03.780  2013-07-19 04:00:03.7800000 -04:00

如果内置函数只是这样做,那将是理想的:

TODATETIMEOFFSET(value)

而不是必须创建一个"过载":

dbo.ToDateTimeOffset(value)

注意:任何代码都将发布到公共域中.无需归属.