Never use GetDate() when comparing date timesoffsets, use SYSDATETIMEOFFSET()

-- my current uk time is 2014-01-09 10:43:00 +0

DECLARE @userLocalTimeChina datetimeoffset(4) = '2014-01-09 18:43:00 +08:00';

DECLARE @userLocalTimeLasVagas datetimeoffset(4) = '2014-01-09 02:43:00 -08:00';

DECLARE @userUTCTime datetimeoffset(4) = '2014-01-09 10:43:00 +00:00';

Declare @systemDateTimeOffsetWhereServerInUK datetimeoffset(4) = SYSDATETIMEOFFSET();

Declare @systemDateTimeWhereServerInUK datetime = GETDATE();

print @systemDateTimeOffsetWhereServerInUK

print @systemDateTimeWhereServerInUK

-- for demo, it gives this

SET @systemDateTimeOffsetWhereServerInUK = '2014-01-09 10:43:00 +00:00';

SET @systemDateTimeWhereServerInUK = '2014-01-09 10:43:00'

Declare @systemDateTimeOffsetWhereServerInNY datetimeoffset(4) = '2014-01-09 05:43:00 -05:00';

Declare @systemDateTimeWhereServerInNY datetime = '2014-01-09 05:43:00';

-- ALL THESE TIMES should be the same.

--Using HOURS here to show the difference, but if we usually use DAYS, this simply means people can 'see' things or 'where clauses' go wrong at certain hours of the day

print 'Compare user LOCAL time to server offset and not offset date time, in uk then new york'

print DATEDIFF(HH, @userLocalTimeChina, @systemDateTimeOffsetWhereServerInUK); -- Correct

print DATEDIFF(HH, @userLocalTimeChina, @systemDateTimeWhereServerInUK); -- The result is correct, but only because server is in UK and no daylight savings time, so will be INCORRECT and CORRECT depending on time of year!!!

print DATEDIFF(HH, @userLocalTimeChina, @systemDateTimeOffsetWhereServerInNY); -- CORRECT

print DATEDIFF(HH, @userLocalTimeChina, @systemDateTimeWhereServerInNY); -- INCORRECT RESULT

print 'Compare user UTC time to server offset and not offset date time, in uk then new york'

-- compare Users UTC time offset with system offset produces CORRECT result most of the time, in the uk

print DATEDIFF(HH, @userUTCTime, @systemDateTimeOffsetWhereServerInUK); -- CORRECT

print DATEDIFF(HH, @userUTCTime, @systemDateTimeWhereServerInUK); -- The result is correct, but only because server is in UK and no daylight savings time, so will be INCORRECT and CORRECT depending on time of year!!!

print DATEDIFF(HH, @userUTCTime, @systemDateTimeOffsetWhereServerInNY); -- CORRECT

print DATEDIFF(HH, @userUTCTime, @systemDateTimeWhereServerInNY); -- INCORRECT RESULT

--CONCLUSION: ALWAYS COMPARE OFFSET TO OFFSET. OR UTCDATETIME TO UTCDATETIME. otherwise it's totaly dependant on the deploy location time zone if the solution will work.