DateTime Precision

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DateTime Precision

jkelly

Right there with Babe

Points: 765
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November 26, 2011 at 5:04 pm

#390959

Comments posted to this topic are about the item DateTime Precision

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Ron McCullough SSC Guru Points: 63877 More actions · Answer 1

As Sherlock Holmes said to Dr. Watson ................ Very interesting

If everything seems to be going well, you have obviously overlooked something.

Ron

Please help us, help you -before posting a question please read[/url]
Before posting a performance problem please read[/url]

M&M SSC-Insane Points: 21700 More actions · Answer 2

M&M

SSC-Insane

Points: 21700

November 27, 2011 at 7:07 am

#1413170

Good observation. Thanks.

M&M

cengland0 SSCertifiable Points: 6102 More actions · Answer 3

Don't you hate it when the explanation says, "Despite what BOL says..."

It should either be mentioned in BOL or do what the BOL says.

Ron McCullough SSC Guru Points: 63877 More actions · Answer 4

cengland0 (11/27/2011)
Don't you hate it when the explanation says, "Despite what BOL says..."
It should either be mentioned in BOL or do what the BOL says.

Heck no one is perfect, and if memory serves me correctly those who write the explanations for BOL are NOT the developers or actual personnel writing the code ...

If everything seems to be going well, you have obviously overlooked something.

Ron

Please help us, help you -before posting a question please read[/url]
Before posting a performance problem please read[/url]

Jostein Saethern SSCommitted Points: 1861 More actions · Answer 5

The question is not really about datetime precision, but string comparison.

If the comparison value had been declared as datetime, then the other values would be implicitly converted to datetime as well and the statement would return Yes.

declare @d as datetime

set @d = '2011-07-31 00:00:00.000'

IF @d BETWEEN '2011-07-01' and '2011-07-31'

PRINT 'Yes'

ELSE

PRINT 'No'

The question as it stands could just as well have been this

if ('abcd' between 'ab' and 'abc')

print 'yes'

else

print 'no'

vk-kirov SSCertifiable Points: 7686 More actions · Answer 6

Nice tricky question with stupid 'explanation'.

Of course, the string (not datetime) '2011-07-31 00:00:00.000' is greater than the other string '2011-07-31', and thus the result of the batch is 'No'.

Stephen E. Cook SSCrazy Points: 2275 More actions · Answer 7

Glad I checked out the comments after getting this one wrong. I hate learning things that aren't true. 🙂

-- Stephen Cook

Koen Verbeeck SSC Guru Points: 259085 More actions · Answer 8

Silly trick question...

Need an answer? No, you need a question
My blog at https://sqlkover.com.
MCSE Business Intelligence - Microsoft Data Platform MVP

SQLWinther SSCertifiable Points: 6294 More actions · Answer 9

Jostein Saethern (11/27/2011)
The question is not really about datetime precision, but string comparison.
If the comparison value had been declared as datetime, then the other values would be implicitly converted to datetime as well and the statement would return Yes.
declare @d as datetime
set @d = '2011-07-31 00:00:00.000'
IF @d BETWEEN '2011-07-01' and '2011-07-31'
PRINT 'Yes'
ELSE
PRINT 'No'
The question as it stands could just as well have been this
if ('abcd' between 'ab' and 'abc')
print 'yes'
else
print 'no'

You are right, I'ts very obvious when you think about it, but when you see something that looks like a date, you assume that SQL server see it as a date. BUT it would be dangerous if SQL server would interpret the datatypes based on the values, and this is just another reason to dislike the implicit conversions. (I know, there is no implicit conversion in the question, but we have learned to live with them so long that we assume it takes place all the time).

I really would like a database setting, a trace flag or something that warn you or prevent you from using implicit conversion and force you to use explicit conversion. Because if you do, you know that you are doing something wrong (from a performance perspective).

The explanation is not correct and should be changed.

/Håkan Winther
MCITP:Database Developer 2008
MCTS: SQL Server 2008, Implementation and Maintenance
MCSE: Data Platform

Iulian -207023 SSCertifiable Points: 7639 More actions · Answer 10

It is a string comparation.

Dates comparation might be:

IF (CAST( '2011-07-31 00:00:00.000' AS DATETIME) BETWEEN CAST( '2011-07-01' AS DATETIME) and CAST( '2011-07-31' AS DATETIME) )

PRINT 'Yes'

ELSE

PRINT 'No'

Regards,

Iulian

paul s-306273 SSChampion Points: 10727 More actions · Answer 11

paul s-306273

SSChampion

Points: 10727

November 28, 2011 at 1:43 am

#1413270

Hi jkelly - tricky question!

Skanker Hall of Fame Points: 3059 More actions · Answer 12

Thanks for the question and also to the posts gave me something to think about on a cold Monday morning.

Paul Urban SSC Rookie Points: 44 More actions · Answer 13

As several people have pointed out, this "explanation" is bogus.

SQL Server is comparing these values as strings - this has nothing to do with datetime precision. Replace the '2011-07-31 00:00:00.000' with '2011-07-31 REDHERRING' and you get the same result.

Sunil Chandurkar Right there with Babe Points: 791 More actions · Answer 14

I overlooked that it is a STRING comparison and got the answer wrong.:-) (though writer had intention to show datetime comparison)

I updated the code as follows and executed:

DECLARE @DATE DATETIME

SET @DATE = '2011-07-31 00:00:00.001'

IF (@DATE BETWEEN '2011-07-01' and '2011-07-31')

PRINT 'Yes'

ELSE

PRINT 'No'

The output came 'Yes'. However when I changed the @date value to '2011-07-31 00:00:00.002' the result was 'No'. As per my knowledge the @date value should be compared to the end date '2011-07-31 00:00:00.000'. How '2011-07-31 00:00:00.001' be less than or equal to '2011-07-31 00:00:00.000'?:unsure:

I executed this on SQL Sever 2008 EE Ver. 10.0.4064.0