SQL Server Journey with SQL Authority

I recently received interesting comment on the blog regarding workaround to overcome the precision issue while dealing with DATETIME and DATETIME2.

I have written over this subject earlier over here.

SQL SERVER – Difference Between GETDATE and SYSDATETIME

SQL SERVER – Difference Between DATETIME and DATETIME2 – WITH GETDATE

SQL SERVER – Difference Between DATETIME and DATETIME2

SQL Expert Jing Sheng Zhong has left following comment:

The issue you found in SQL server new datetime type is related time source function precision. Folks have found the root reason of the problem – when data time values are converted (implicit or explicit) between different data type, which would lose some precision, so the result cannot match each other as thought. Here I would like to gave a work around solution to solve the problem which the developers met.

-- Declare and loop
DECLARE @Intveral INT, @CurDate DATETIMEOFFSET;
CREATE TABLE #TimeTable (FirstDate DATETIME, LastDate DATETIME2, GlobalDate DATETIMEOFFSET)
SET @Intveral = 10000
WHILE (@Intveral > 0)
BEGIN
----SET @CurDate = SYSDATETIMEOFFSET(); -- higher precision for future use only
SET @CurDate = TODATETIMEOFFSET(GETDATE(),DATEDIFF(N,GETUTCDATE(),GETDATE())); -- lower precision to match exited date process
INSERT #TimeTable (FirstDate, LastDate, GlobalDate)
VALUES (@CurDate, @CurDate, @CurDate)
SET @Intveral = @Intveral - 1
END
GO
-- Distinct Values
SELECT COUNT(DISTINCT FirstDate) D_DATETIME,
COUNT(DISTINCT LastDate) D_DATETIME2,
COUNT(DISTINCT GlobalDate) D_SYSGETDATE
FROM #TimeTable
GO
-- Join
SELECT DISTINCT a.FirstDate,b.LastDate, b.GlobalDate, CAST(b.GlobalDate AS DATETIME) GlobalDateASDateTime
FROM #TimeTable a
INNER JOIN #TimeTable b ON a.FirstDate = CAST(b.GlobalDate AS DATETIME)
GO
-- Select
SELECT *
FROM #TimeTable
GO
-- Clean up
DROP TABLE #TimeTable
GO


If you read my blog SQL SERVER – Difference Between DATETIME and DATETIME2 you will notice that I have achieved the same using GETDATE().

Are you using DATETIME2 in your production environment? If yes, I am interested to know the use case.

Reference: Pinal Dave (http://www.SQLAuthority.com)

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Earlier I wrote about SQL SERVER – Datetime Function SWITCHOFFSET Example. After reading this blog post, I got another quick reply that if I can explain the usage of TODATETIMEOFFSET as well.

Let us go over the definition of the TODATETIMEOFFSET  from BOL: Returns a datetimeoffset value that is translated from a datetime2 expression.

What essentially it does is that changes the current offset only  offset which we defined. Let us see the example of the same.

SELECT SYSDATETIMEOFFSET() GetCurrentOffSet;
SELECT TODATETIMEOFFSET(SYSDATETIMEOFFSET(), '-04:00') 'GetCurrentOffSet-4';
SELECT TODATETIMEOFFSET(SYSDATETIMEOFFSET(), '-02:00') 'GetCurrentOffSet-2';
SELECT TODATETIMEOFFSET(SYSDATETIMEOFFSET(), '+00:00') 'GetCurrentOffSet+0';
SELECT TODATETIMEOFFSET(SYSDATETIMEOFFSET(), '+02:00') 'GetCurrentOffSet+2';
SELECT TODATETIMEOFFSET(SYSDATETIMEOFFSET(), '+04:00') 'GetCurrentOffSet+4';

Let us see the resultset below.

It is quite clear from the example that only offset changes in the time but unlike SWITCHOFFSET the datetime remains the same.

Reference : Pinal Dave (http://blog.SQLAuthority.com)

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I was recently asked if I know how SWITCHOFFSET works. This feature only works in SQL Server 2008.

Here is quick definition of the same from BOL: Returns a datetimeoffset value that is changed from the stored time zone offset to a specified new time zone offset.

What essentially it does is that changes the current offset of the time to any other offset which we defined. Let us see the example of the same.

SELECT SYSDATETIMEOFFSET() GetCurrentOffSet;
SELECT SWITCHOFFSET(SYSDATETIMEOFFSET(), '-04:00') 'GetCurrentOffSet-4';
SELECT SWITCHOFFSET(SYSDATETIMEOFFSET(), '-02:00') 'GetCurrentOffSet-2';
SELECT SWITCHOFFSET(SYSDATETIMEOFFSET(), '+00:00') 'GetCurrentOffSet+0';
SELECT SWITCHOFFSET(SYSDATETIMEOFFSET(), '+02:00') 'GetCurrentOffSet+2';
SELECT SWITCHOFFSET(SYSDATETIMEOFFSET(), '+04:00') 'GetCurrentOffSet+4';

Now let us check the resultset of the same.

The example above clearly shows that Switch offset does not only change the offset; it also alters the current time. If you look at GetcurrentOffset, it is +5.30; but, you will notice that GetCurrentOffset-2 does not only change the offset to -2. It also changes the time with the appropriate time at Timezone -2.

I suggest that you run the code in SSMS Query Window and observe the code behavior.

Reference: Pinal Dave (http://blog.SQLAuthority.com)

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Earlier I wrote blog post SQL SERVER – Difference Between GETDATE and SYSDATETIME which inspired me to write SQL SERVER – Difference Between DATETIME and DATETIME2. Now earlier two blog post inspired me to write this blog post (and 4 emails and 3 reads from readers).

I previously populated DATETIME and DATETIME2 field with SYSDATETIME, which gave me very different behavior as SYSDATETIME was rounded up/down for the DATETIME datatype. I just ran the same experiment but instead of populating SYSDATETIME in this script I will be using GETDATE function.
DECLARE @Intveral INT
SET @Intveral = 10000
CREATE TABLE #TimeTable (FirstDate DATETIME, LastDate DATETIME2)
WHILE (@Intveral > 0)
BEGIN
INSERT #TimeTable (FirstDate, LastDate)
VALUES (GETDATE(), GETDATE())
SET @Intveral = @Intveral - 1
END
GO
SELECT COUNT(DISTINCT FirstDate) D_FirstDate, COUNT(DISTINCT LastDate) D_LastDate
FROM #TimeTable
GO
SELECT DISTINCT a.FirstDate, b.LastDate
FROM #TimeTable a
INNER JOIN #TimeTable b ON a.FirstDate = b.LastDate
GO
SELECT *
FROM #TimeTable
GO
DROP TABLE #TimeTable
GO

Let us run above script and observe the results.

You will find that the values of GETDATE which is populated in both the columns FirstDate and LastDate are very much same. This is because GETDATE is of datatype DATETIME and the precision of the GETDATE is smaller than DATETIME2 there is no rounding happening.

In other word, this experiment is pointless. I have included this as I got 4 emails and 3 twitter questions on this subject. If your datatype of variable is smaller than column datatype there is no manipulation of data, if data type of variable is larger than column datatype the data is rounded.

Reference: Pinal Dave (http://www.SQLAuthority.com)

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