On Mon, Oct 13, 2008 at 6:33 AM, Gregory Stark <stark@enterprisedb.com> wrote:
> justin <justin@emproshunts.com> writes:
>
>> special note do not use only 2 decimal points in the accounting tables. If
>> your application uses 10 decimal places somewhere then every table in the
>> database that has decimals needs to have the same precision. Nothing is more
>> annoying where a transaction says 1.01 and the other side says 1.02 due to
>> rounding.
>
> FWIW I think this is wrong. You need to use precisely the number of decimal
> places that each datum needs. If you use extra it's just as wrong as if you
> use too few.
>
> For example, when you buy gas/petrol at $1.999/gallon and buy 4 gallons you
> get charged $8.00 not $7.996. If you fail to round at that point you'll find
> that your totals don't agree with the amount of money in your actual bank
> account.
I wonder if there's a more general way to say that, something like:
With a transaction between two systems of different precision, the
greater precision system rounds at that point.
If you want to take a particular system out to extra digits, it's
probably good to record the rounding error as a separate component of
the transaction (that is, if you want everything to balance out
perfectly).
merlin
