"Yonatan Ben-Nes" <yonatan@epoch.co.il> writes:
> Hi all, I need to decide which data type should I make for monetary values,
> shall I use Numeric data type to hold values like "9.52" or is it better to
> keep it as an integer with value in cents like "952"? I know that at the
> manual it's written about the Numeric data type that "It is especially
> recommended for storing monetary amounts and other quantities where
> exactness is required.", but I'm wondering what will happen at cases when I
> got $1.01 to divide between 2 entities at 50% each, if both will get 51
> cents or 50 cents it will be a mistake. The calculation procedure will
> probably be made with PL/pgSQL, actually maybe it doesn't even matter what
> the data type is (Integer/Numeric) as long as I make enough validations for
> the result?
You'll have the problem with any of these data type unless you have enough
precision stored. To make it work you shouldn't store cents but smaller
fractions of it.
I use numeric with at least 4 digits after the comma. When I need some input
or need to show the user some information I show only two digits as it is
usual. Sometimes I allow them to work with 4 digits as well.
Here in Brazil fuel is sold using 3 decimal places (e.g. 2.597 reais per
liter of gasoline) so I'd need at least that precision anywhere I was going to
deal with fuel costs.
With regards to inexact fractions, what happens depends on the law of the
country. The law here determinates that the value should be truncated to two
decimal places. If I bought one liter of gasoline I should pay 2.59 reais and
not 2.60. There are places where you could have rounding (e.g. calculations
inside a company) instead of truncation...
Dealing with money is a really complex subject and requires a lot of planning.
My recommendation is to get two decimal places more than needed to avoid
rounding issues (and if you need truncation, the truncate only at the very end
where you'll have minimum loss).
--
Jorge Godoy <jgodoy@gmail.com>