SQL Server - Convert date field to UTC

Question

I have recently updated my system to record date/times as UTC as previously they were storing as local time.

I now need to convert all the local stored date/times to

Answer 1

I'm a bit late to the game but I needed to do something like this on SQL 2012, I haven't fully tested it yet but here is what I came up with.

CREATE FUNCTION SMS.fnConvertUTC
(
    @DateCST datetime
)
RETURNS DATETIME
AS
BEGIN
    RETURN 
        CASE 
        WHEN @DateCST 
            BETWEEN 
                CASE WHEN @DateCST > '2007-01-01' 
                THEN CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(@DateCST)) + '-MAR-14 02:00') - DATEPART(DW,CONVERT(VARCHAR,YEAR(@DateCST)) + '-MAR-14 02:00' ) + 1
                ELSE CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(@DateCST)) + '-APR-07 02:00') - DATEPART(DW,CONVERT(VARCHAR,YEAR(@DateCST)) + '-APR-07 02:00' ) + 1 END
            AND
                CASE WHEN @DateCST > '2007-01-01' 
                THEN CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(@DateCST)) + '-NOV-07 02:00') - DATEPART(DW,CONVERT(VARCHAR,YEAR(@DateCST)) + '-NOV-07 02:00' ) + 1
                ELSE CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(@DateCST)) + '-OCT-31 02:00') - DATEPART(DW,CONVERT(VARCHAR,YEAR(@DateCST)) + '-OCT-31 02:00' ) + 1 END
        THEN DATEADD(HOUR,4,@DateCST)
        ELSE DATEADD(HOUR,5,@DateCST) 
        END
END

Above someone posted a static list DST dates so I wrote the below query to compare this code's output to that list... so far it looks correct.

;WITH DT AS 
( 
    SELECT MyDate = GETDATE() 
    UNION ALL 
    SELECT MyDate = DATEADD(YEAR,-1,MyDate) FROM DT
    WHERE DATEADD(YEAR,-1,MyDate) > DATEADD(YEAR, -30, GETDATE())
)
SELECT 
    SpringForward = CASE 
        WHEN MyDate > '2007-01-01' 
        THEN CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(MyDate)) + '-MAR-14 02:00') - DATEPART(DW,CONVERT(VARCHAR,YEAR(MyDate)) + '-MAR-14 02:00' ) + 1
        ELSE CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(MyDate)) + '-APR-07 02:00') - DATEPART(DW,CONVERT(VARCHAR,YEAR(MyDate)) + '-APR-07 02:00' ) + 1 END
,   FallBackward  = CASE 
        WHEN MyDate > '2007-01-01' 
        THEN CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(MyDate)) + '-NOV-07 02:00') - DATEPART(DW,CONVERT(VARCHAR,YEAR(MyDate)) + '-NOV-07 02:00' ) + 1
        ELSE CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(MyDate)) + '-OCT-31 02:00') - DATEPART(DW,CONVERT(VARCHAR,YEAR(MyDate)) + '-OCT-31 02:00' ) + 1 END
FROM DT
ORDER BY 1 DESC

SpringForward      FallBackward
----------------   ----------------
2020-03-08 02:00   2020-11-01 02:00
2019-03-10 02:00   2019-11-03 02:00
2018-03-11 02:00   2018-11-04 02:00
2017-03-12 02:00   2017-11-05 02:00
2016-03-13 02:00   2016-11-06 02:00
2015-03-08 02:00   2015-11-01 02:00
2014-03-09 02:00   2014-11-02 02:00
2013-03-10 02:00   2013-11-03 02:00
2012-03-11 02:00   2012-11-04 02:00
2011-03-13 02:00   2011-11-06 02:00
2010-03-14 02:00   2010-11-07 02:00
2009-03-08 02:00   2009-11-01 02:00
2008-03-09 02:00   2008-11-02 02:00
2007-03-11 02:00   2007-11-04 02:00
2006-04-02 02:00   2006-10-29 02:00
2005-04-03 02:00   2005-10-30 02:00
2004-04-04 02:00   2004-10-31 02:00
2003-04-06 02:00   2003-10-26 02:00
2002-04-07 02:00   2002-10-27 02:00
2001-04-01 02:00   2001-10-28 02:00
2000-04-02 02:00   2000-10-29 02:00
1999-04-04 02:00   1999-10-31 02:00
1998-04-05 02:00   1998-10-25 02:00
1997-04-06 02:00   1997-10-26 02:00
1996-04-07 02:00   1996-10-27 02:00
1995-04-02 02:00   1995-10-29 02:00
1994-04-03 02:00   1994-10-30 02:00
1993-04-04 02:00   1993-10-31 02:00
1992-04-05 02:00   1992-10-25 02:00
1991-04-07 02:00   1991-10-27 02:00

(30 row(s) affected)