Re: Bug #644: Incorrect result in math operation

Hi!

On Wed, 24 Apr 2002 04:33:00 -0400 (EDT)
pgsql-bugs(at)postgresql(dot)org wrote:

> Francisco Blay (franblay(at)ono(dot)com) reports a bug with a severity of 3
> The lower the number the more severe it is.
>
> Short Description
> Incorrect result in math operation
>
> Long Description
> 3088.8 - (2847.64 + 241.16)=4.54747350886464e-13
> It's spected to be 0.0 the result of this operation (I think)
> Got the same results in
>
...
> datadb=# select 3088.8 - (2847.64 + 241.16) AS silly;
> silly
> ----------------------
> 4.54747350886464e-13
> (1 row)
>

I think it's a limitation of floating point numbers representation, not a PostgreSQL bug. Use NUMERIC type, if you need an "exact" precision:

org=> SELECT 3088.8::numeric(8,3) - (2847.64::numeric(8,3) + 241.16::numeric(8,3)) AS silly;
silly
-------
0.000
(1 row)

Best regards

--
Dmitry Tsitelov
mailto:cit(at)tag-ltd(dot)spb(dot)ru