SQL Server 2008 new datetime types, functions and the conversions

Datetime Types in SQL Server 2005:
Lets start with a quick look at the existing date time types in SQL Server. The datetime and smalldatetime, these two types are well known to us, So we wont be spending much time here.

Data Type	Representation	Accuracy
smalldatetime	YYYY-MM-DD hh:mm:ss	1 minute
datetime	YYYY-MM-DD hh:mm:ss[.nnn]	0.00333 second

Though these types provide a whole lot of datetime functionality required for any database. The problem is that the date representation is always combined with the time in both the types and there is no way to represent the date only component or time only component in a database with out doing a lot of cast and convert.

New Datetime Types in SQL Server 2008
SQL Server 2008 has introduced four new datetime data types for the date and time representations in SQL Server Databases.

Data Type	Representation	Accuracy
date	YYYY-MM-DD	1 day
time[n]	hh:mm:ss[.nnnnnnn]	100 nanoseconds
datetime2[n]	YYYY-MM-DD hh:mm:ss[.nnnnnnn]	100 nanoseconds
datetimeoffset[n]	YYYY-MM-DD hh:mm:ss[.nnnnnnn] [+|-]hh:mm	100 nanoseconds

The new Date type allows us to represents the date as an individual component with out the time field attached to it. And the Time type represents the Time as an individual component in databases. Note that the new Time type is at higher precision than the regular time in datetime type.

Datetime2 can be considered as an extension to regular datetime type with the time representation at an accuracy of 100 nanoseconds than at the regular 0.00333 seconds. The datetime2 type can be used with a default precision (datetime2(7)) or can be used with a user defined precision like datetime2(n) format. If the time precision of datetime2 is set to 3 (datetime2(3)) which gives the exact equivalent representation of a regular datetime type.

DateTimeOffset is the combination of default datetime2 with the system time zone offset attached to it. The time zone offset displayed based on the Operating System date, time and culture settings. The offset should be between –14:00 to +14:00. The DateTimeOffset type does not support the day light saving times.

Here is my machine current datetimeoffset value 2010-04-25 23:24:07.7086518 +05:30. Notice that the time zone offset returned is +05:30 i.e. IST (Indian Standard Time) attached to datetime2 data.

New Date and Time Functions

SYSDATETIME()	Similar to GETDATE() but it returns the current system date as new datetime2(7) type
SYSUTCDATETIME()	Similar to GETUTCDATE() but it returns the current system date in UTC as a new datetime2(7) type
SYSDATETIMEOFFSET()	Returns the current system date time as DateTime2(7) with system time zone offset attached to it
SWITCHOFFSET(expr, tz)	Function to convert the datetimeoffset in one time zone to a datetimeoffset in another timezone
TODATETIMEOFFSET(expr, tz)	Function to convert the datetime, datetime2 or datetimeoffset to a datetimeoffset with the specified time zone

Conversions between different datetime types
1. How to convert datetime or datetime2 to datetimeoffset with specified time zone?

SELECT GETDATE(), TODATETIMEOFFSET(GETDATE(), '+08:30')
 -- results: 2010-04-26 00:18:36.927  | 2010-04-26 00:18:36.927 +08:30

SELECT SYSDATETIME(), TODATETIMEOFFSET(SYSDATETIME(), '+05:30')
-- results: 2010-04-26 00:18:36.9316407 | 2010-04-26 00:18:36.9316407 +05:30

TODATETIMEOFFSET() combines the specified datetime or datetime2 to the specified time zone offset.

2. How to convert the datetimeoffset in one time zone to datetimeoffset in other time zone?

-- my current system time in IST (GMT + 5:30)
SELECT SYSDATETIMEOFFSET()
       -- 2010-04-26 00:32:48.1838343 +05:30

-- IST (GMT + 5:30) converted to North America PST (GMT - 8:00)
SELECT SWITCHOFFSET(SYSDATETIMEOFFSET(), '-08:00')
       -- 2010-04-25 11:02:48.1838343 -08:00

-- IST (GMT + 5:30) converted to Europe BST (GMT + 1:00)
SELECT SWITCHOFFSET(SYSDATETIMEOFFSET(), '+01:00')
       -- 2010-04-25 20:02:48.1838343 +01:00

3. How to convert local datetime or datetime2 to UTC (Coordinated Universal Time)?

DECLARE @LocalDateTime datetime
DECLARE @TimeZoneOffset INT

-- convert my current system datetime to UTC
SET @LocalDateTime = GETDATE()
     -- 2010-04-26 00:44:19.107

-- get the timezone offset of the system
SET @TimeZoneOffset = DATEDIFF(MI, SYSDATETIME(),SYSUTCDATETIME())
     -- 330 mins (i.e. 5:30 )

-- get the utc datetime
SELECT DATEADD(MI,@TimeZoneOffset, @LocalDateTime)
      -- 2010-04-25 19:14:19.107 

4. How to convert datetimeoffset to UTC?

DECLARE @DTO DATETIMEOFFSET
-- convert my system datetimeoffset to UTC
SET @DTO = SYSDATETIMEOFFSET()
-- 2010-04-26 00:50:35.3701337 +05:30

-- switch offset to '+00:00' i.e. UTC
SELECT SWITCHOFFSET(@DTO, '+00:00')
      ,CAST(SWITCHOFFSET(@DTO, '+00:00') AS DATETIME2)
-- 2010-04-25 19:20:35.3701337 +00:00  | 2010-04-25 19:20:35.3701337

5. Other simple conversions?

SELECT CAST(GETDATE() AS Time)
      ,CAST(GETDATE() as date)
      ,CAST(SYSDATETIMEOFFSET() AS datetime2)
 -- results: 01:03:35.5700000 | 2010-04-26 | 2010-04-26 01:03:35.5971486

-- get timezone offset from datetimeoffset
SELECT DATEPART(TZ, SYSDATETIMEOFFSET())
 -- results: 330 (number of minutes)

The new date time types in SQL Server 2008 are more portable than datetime or smalldatetime and it is recommended to use them in the future development work.