Обсуждение: BUG #3959: Huge calculation error

The following bug has been logged online:

Bug reference:      3959
Logged by:          Renaud Diez
Email address:      rdiez@salesprize.com
PostgreSQL version: 8.2
Operating system:   Debian
Description:        Huge calculation error
Details:

the basic mathematical expression like the following one doesn't compute the
correct result:

> select 100*(1+(21/100));

return a result of 100 instead of 121.

Renaud Diez wrote:
> The following bug has been logged online:
>
> Bug reference:      3959
> Logged by:          Renaud Diez
> Email address:      rdiez@salesprize.com
> PostgreSQL version: 8.2
> Operating system:   Debian
> Description:        Huge calculation error
> Details:
>
> the basic mathematical expression like the following one doesn't compute the
> correct result:
>
>> select 100*(1+(21/100));
>
> return a result of 100 instead of 121.

It does compute the correct result, because you're doing integer
calculations. 21/100 for integers is 0. To make it do float calc, you can do
select 100*(1+(21::float/100));

Or you can do
select 100*(1+(21.0/100));

which will force it to numeric.

//Magnus

Renaud Diez wrote:
> The following bug has been logged online:
>
> Bug reference:      3959
> Logged by:          Renaud Diez
> Email address:      rdiez@salesprize.com
> PostgreSQL version: 8.2
> Operating system:   Debian
> Description:        Huge calculation error
> Details:
>
> the basic mathematical expression like the following one doesn't compute the
> correct result:
>
>> select 100*(1+(21/100));
>
> return a result of 100 instead of 121.

That's because 21/100 = 0, in integer math. Try "SELECT
100*(1+(21/100.0))" to use floating points.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

Renaud Diez wrote:
> The following bug has been logged online:
>
> Bug reference:      3959
> Logged by:          Renaud Diez
> Email address:      rdiez@salesprize.com
> PostgreSQL version: 8.2
> Operating system:   Debian
> Description:        Huge calculation error
> Details:
>
> the basic mathematical expression like the following one doesn't compute the
> correct result:
>
>
>> select 100*(1+(21/100));
>>
>
> return a result of 100 instead of 121.
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
>
>
Hola, en realidad no lo hace mal, no es lo que esprabas, lo que en
realidad necesitas es esto:
select 100*(1+(21.0/100))::float;
saludos Fernando