Strange SQL calculation error

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SQL-Server-2005

Hi
I'm using MS SQL Server 2005.Check out the below query.

SQL

declare @str float
select  @str =convert(float,isnull(30452.8885,0)) * convert(float,isnull(219.8700,0))
select convert(decimal(38,10),@str) A,@str B

If we do the above multiplication using any calculator we will get B(6695676.594495) as output.
But then when we convert the multiplication of two values to decimal(38,10), sql gives 6695676.5944950003 as A, which is strange.
How can 6695676.594495 when converted to decimal(38,10) give 6695676.5944950003?

Any idea how this strange calculation happens?

Regards,
Sunit.

Posted 29-Sep-11 2:06am

sunit_82

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CPallini · Answer 1 · 2011-09-29T02:19:00

floating point values contains approximations of decimal numbers (values are store in binary form, using a finite number of bits, see "IEEE 754 Wikipedia page"[^] for detailed info).
You may verify that the following C++ program produces the same ouput:

C++

#include<iostream> 
#include <iomanip>
#include<cstdlib> 
using namespace std; 
int main()
{
  double a = 30452.8885;
  double b = 219.8700;
  double k = a * b;
  cout << setprecision(30) << k << endl;
}