Effectively Converting dates between UTC and Local (ie. PST) time in SQL 2005

What is the best way to convert a UTC datetime into local datetime. It isn’t as simple as a getutcdate() and getdate() difference because the difference changes depending on what the date is.

CLR integration isn’t an option for me either.

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  • The solution that I had come up with for this problem a few months back was to have a daylight savings time table that stored the beginning and ending daylight savings days for the next 100 or so years, this solution seemed inelegant but conversions were quick (simple table lookup)

    11 Solutions collect form web for “Effectively Converting dates between UTC and Local (ie. PST) time in SQL 2005”

    Create two tables and then join to them to convert stored GMT dates to local time:

    TimeZones     e.g.
    ---------     ----
    TimeZoneId    19
    Name          Eastern (GMT -5)
    Offset        -5
    

    Create the daylight savings table and populate it with as much information as you can (local laws change all the time so there’s no way to predict what the data will look like years in the future)

    DaylightSavings
    ---------------
    TimeZoneId    19
    BeginDst      3/9/2008 2:00 AM
    EndDst        11/2/2008 2:00 AM
    

    Join them like this:

    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
    

    Convert dates like this:

    dateadd(hh, tz.Offset + 
        case when ds.LocalTimeZone is not null 
        then 1 else 0 end, TheDateToConvert)
    

    If you’re in the US and only interested in going from UTC/GMT to a fixed time zone (such as EDT) this code should suffice. I whipped it up today and believe it’s correct but use at your own risk.

    Adds a computed column to a table ‘myTable’ assuming your dates are on the ‘date’ column. Hope someone else finds this useful.

    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)
    

    A much simpler and generic solution that considers daylight savings. Given an UTC date in “YourDateHere”:

    --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]
    

    If either of these issues affects you, you should never store local times in the database:

    1. With DST is that there is an “hour of uncertainty” around the falling back period where a local time cannot be unambiguously converted. If exact dates & times are required, then store in UTC.
    2. If you want to show users the date & time in their own timezone, rather than the timezone in which the action took place, store in UTC.

    In Eric Z Beard’s answer, the following 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 
    

    might more accurately be:

    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 
    

    (above code not tested)

    The reason for this is that the sql “between” statement is inclusive. On the back-end of DST, this would result in a 2AM time NOT being converted to 1AM. Of course the likelihood of the time being 2AM precisely is small, but it can happen, and it would result in an invalid conversion.

    FOR READ-ONLY Use this(inspired by Bob Albright’s incorrect solution ):

    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
    

    I posted this answer after I tried to edit Bob Albright’s wrong answer. I corrected the times and removed superfluous abs(), but my edits were rejected multiple times. I tried explaining, but was dismissed as a noob. His is a GREAT approach to the problem! It got me started in the right direction. I hate to create this separate answer when his just needs a minor tweak, but I tried ¯\_(ツ)_/¯

    Maintain a TimeZone table, or shell out with an extended stored proc (xp_cmdshell or a COM component, or your own) and ask the OS to do it. If you go the xp route, you’d probably want to cache the offset for a day.

    I like the answer @Eric Z Beard provided.

    However, to avoid performing a join everytime, what about this?

    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
    

    Then

     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)
    

    finally becoming

     dateadd(hh, @offset, TheDateToConvert)
    

    I’ve read through a lot of StackOverflow posts in regards to this issue and found many methods. Some “sort of” ok. I also found this MS reference (https://msdn.microsoft.com/en-us/library/mt612795.aspx) which I tried to utilize in my script. I have managed to achieve the required result BUT I am not sure if this will run on 2005 version. Either way, I hope this helps.

    Fnc to return PST from the system UTC default

    CREATE FUNCTION dbo.GetPst()
    RETURNS DATETIME
    AS 
    BEGIN
    
        RETURN  SYSDATETIMEOFFSET() AT TIME ZONE 'Pacific Standard Time'
    
    END
    
    SELECT dbo.GetPst()
    

    Fnc to return PST from the provided timestamp

    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')
    

    I am using this because all of my dates are from now forward.

    DATEADD(HH,(DATEPART(HOUR, GETUTCDATE())-DATEPART(HOUR, GETDATE()))*-1, GETDATE())
    

    For historical dates (or to handle future changes in DST, I’m guessing Bob Albright’s solution would be the way to go.

    The modification I make to my code is to use the target column:

    DATEADD(HH,(DATEPART(HOUR, GETUTCDATE())-DATEPART(HOUR, GETDATE()))*-1, [MySourceColumn])
    

    So far, this seems to work, but I’m happy to receive feedback.

    Here is the code I use to make my timezone table. It’s a bit naive, but is usually good enough.

    Assumptions:

    1. It assumes US only rules (DST is 2AM on some pre-defined Sunday,
      etc).
    2. It assumes you don’t have dates prior to 1970
    3. It assumes you know the local timezone offsets (i.e.: EST=-05:00, EDT=-04:00, etc.)

    Here’s the 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
    
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