Re: Strange round behaviour w/ more than 2 decimals

Hi Tom,

Sorry. After sending to group one friend of mine explained to me how round
works -- not postgresql round, but round in math.
I do not know any software that would produce that output.

I thought that when 1.8947 was rounded to 2 decimal places, 7 would round-up
4, then "5" would round-up 9.

Reading http://www.ai.com.br/pessoal/indices/2A1A.HTM show the correct way
(sorry, the page is in brazilian portuguese).

Anyway, the document shows: DO NOT DO RECURSIVE ROUNDS! hehe.

Thanks for the answer and sorry for the incorrect question.

Regards,
Fernando Pinheiro

2007/7/11, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
>
> "Fernando Madruga Pinheiro" <fernando(dot)madrugapinheiro(at)gmail(dot)com> writes:
> > If I use ROUND(1.8947, 2), it should return 1.90, but it does return
> 1.89.
>
> Why do you consider that wrong? It's the closest approximation.
> Do you know of any other software that would produce 1.90 from a
> similar query?
>
> > Rounding to 3 decimal places, then 2 (eg.: ROUND(ROUND(1.8947, 3), 2) )
> then
> > I get 1.90!
>
> Since ROUND() is a lossy process by definition, you cannot expect
> that different multi-step paths will always yield the same result.
>
> regards, tom lane
>