Re: Inconsistent results for division and multiplication operations

On Mon, Nov 25, 2024 at 5:18 PM szy <598546998(at)qq(dot)com> wrote:

> If the number of significant digits in the input is not fixed, it becomes
> challenging to achieve consistent results by rounding.
> for example
> postgres=# select round(1.003/1.002*5.01,2);
> ?column?
> --------------------------
> 5.01
> (1 row)
>
> postgres=# select round(1.003*5.01/1.002,2);
> ?column?
> --------------------
> 5.02
> (1 row)
>
>
Correct. That's why you should always use numeric with the desired
precision if you want precision numbers.

for instance
select 1.003/1.002*5.01 :: numeric(10,4)
will give the same result as
select 1.003*5.01/1.002 :: numeric(10,4)

They are much slower to calculate than floating point, however, so if you
don't care about precision you can keep using just floating point.

Regards,

Martin

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Martin Norbäck Olivers
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