How to calculate the local datetime from a utc datetime in tsql (sql 2005)?

Question

i want to loop over a period of time in tsql, and print the utc datetimes and our local variant. We live in UTC +1, so i could easily add 1 hour, but in the summertime we live i

Answer 1

I recently had to do the same thing. The trick is figuring out the offset from UTC, but it's not a hard trick. You simply use DateDiff to get the difference in hours between local and UTC. I wrote a function to take care of this.

Create Function ConvertUtcDateTimeToLocal(@utcDateTime DateTime)
Returns DateTime
Begin
    Declare @utcNow DateTime
    Declare @localNow DateTime
    Declare @timeOffSet Int

    -- Figure out the time difference between UTC and Local time
    Set @utcNow = GetUtcDate()
    Set @localNow = GetDate()
    Set @timeOffSet = DateDiff(hh, @utcNow, @localNow) 

    DECLARE @localTime datetime 

    Set @localTime = DateAdd(hh, @timeOffset, @utcDateTime) 

    -- Check Results
    return @localTime 

End
GO

This does have on crucial short coming: If a time zone uses a fractional offset, such as Nepal which is GMT+5:45, this will fail because this only deals with whole hours. However, it should fit your needs just fine.