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

If they're all local to you, then here's the offset:

SELECT GETDATE() AS CurrentTime, GETUTCDATE() AS UTCTime

and you should be able to update all the data using:

UPDATE SomeTable
   SET DateTimeStamp = DATEADD(hh, DATEDIFF(hh, GETDATE(), GETUTCDATE()), DateTimeStamp)

Would that work, or am I missing another angle of this problem?