Sql Server Datetime Offset SWITCHOFFSET AT TIME ZONE

--AT TIME ZONE: time and offset are calculated for given timezone
--SWITCHOFFSET: only offset is changed, time remains the same


--create example table _dto for datetimeoffset demo
CREATE TABLE [dbo].[_dto](
[id] [int] IDENTITY(1,1) NOT NULL,
[dtoUtc] [datetimeoffset](7) NULL, --utc time
[dtoLocal] [datetimeoffset](7) NULL --local time
) ON [PRIMARY]
GO

--insert winter and sommertime demo test record
INSERT [dbo].[_dto] ( [dtoUtc]) VALUES (CAST(N'2018-01-23T10:00:00.0000000+00:00' AS DateTimeOffset)) -- winter time
GO
INSERT [dbo].[_dto] ([dtoUtc]) VALUES (CAST(N'2017-07-23T10:00:00.0000000+00:00' AS DateTimeOffset)) -- summer time
GO

--get string values for available sql server time zones:
select * from sys.time_zone_info;

--show result of SWITCHOFFSET and AT TIME ZONE
select dtoUtc ,  --original Utc Time (offset 00)
   SWITCHOFFSET(dtoUtc,1) as switch, -- time remains the same, only offset changes
   dtoUtc AT TIME ZONE 'Central Europe Standard Time' as AtTimeZone -- time and offset are transfered to destination time zone, winter and summer time are calculated correct
from _dto order by dto

--update _dto set dtoLocal= dtoUtc AT TIME ZONE 'Central Europe Standard Time' -- calculating local time from utc and store it
select * from  _dto

--drop table _dto; --clean up