ROUND() function doesn't round properly

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ROUND() function doesn't round properly

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ESB

Posted Friday, October 02, 2009 4:00 AM

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Hello. I use SQL Server 2005 and I'm calculating the age of patients in the following manner:

DATEDIFF(DAY, birthdate, operationdate)/365.25

The output always seems to be a decimal with 6 decimal digits. The rounding problem arises with border cases like for instance an age of 60.444445. If you round this properly it should result in 60.45 and that should result in 60.5. However, when I use ROUND(60.444445, 1) it results in 60.4!

The problem is that SQL Server seems to ignore the digits after the rounding border. ROUND(60.449999, 1) for instance also results in 60.4. It seems to truncate it 1 position behind the rounding index and starts rounding after that.

I found out that using the ROUND() function repeatedly in the following manner solves the issue but it is a bit ridiculous:

PRINT ROUND(ROUND(ROUND(ROUND(ROUND(60.444445, 5), 4), 3), 2), 1)

Is there any other way to solve this and am I missing something?

Thanks in advance!

Post #796803

Dave Ballantyne

Posted Friday, October 02, 2009 4:16 AM

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Heres how to calculate an age

select CASE
WHEN dateadd(year, datediff (year, d1, d2), d1) > d2
THEN datediff (year, d1, d2) - 1
ELSE datediff (year, d1, d2)
END as Age

I'll take a look at the rounding issue though...

Clear Sky SQL
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Post #796805

Dave Ballantyne

Posted Friday, October 02, 2009 4:33 AM

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I think you are wrong in your assessment of round though,

round(60.444445,1) = 60.4

This

PRINT ROUND(ROUND(ROUND(ROUND(ROUND(60.444445, 5), 4), 3), 2), 1)

works because you are rounding a rounded , rounded, rounded , rounded number (ie the 5 has for want of a better word been cascaded up)

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Post #796810

ESB

Posted Friday, October 02, 2009 6:40 AM

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For some reason that way of rounding was in my head. But I spoke with others about and I think SQL Server does round it correctly yes.

Post #796835

Jeff Moden

Posted Friday, October 02, 2009 7:38 PM

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Dave Ballantyne (10/2/2009)

Heres how to calculate an age

select CASE
WHEN dateadd(year, datediff (year, d1, d2), d1) > d2
THEN datediff (year, d1, d2) - 1
ELSE datediff (year, d1, d2)
END as Age

I'll take a look at the rounding issue though...

That's one of the simplest I've seen. Correctly handles the Feb 29 problem that most other's don't handle, too!

--Jeff Moden

"RBAR is pronounced "ree-bar" and is a "Modenism" for "Row-By-Agonizing-Row".

First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column."

For better, quicker answers on T-SQL questions, click on the following...
http://www.sqlservercentral.com/articles/Best+Practices/61537/

For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/

Post #797330

Dave Ballantyne

Posted Monday, October 05, 2009 2:34 AM

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Cant take the credit for it ...

http://windowsitpro.com/article/articleid/14267/how-can-i-calculate-someones-age-in-sql-server.html

Clear Sky SQL
My Blog
Kent user group

Post #797711

Jeff Moden

Posted Monday, October 05, 2009 5:58 AM

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Shoot... the link is broken. Thanks anyway, Dave.

--Jeff Moden

Post #797801

Dave Ballantyne

Posted Monday, October 05, 2009 7:05 AM

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Seems fine now, just a temporary thing i guess.

TBH , its hardly worth the click though Smile

simple Q and A

Clear Sky SQL
My Blog
Kent user group

Post #797849

Jeff Moden

Posted Monday, October 05, 2009 7:08 AM

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Hmmmm.... something must be wrong on my end. It keeps giving me a 404 error.

Q & A's are sometimes pretty rich in information like the little date jewel you found.

--Jeff Moden

Post #797855

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