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Hello, i have the following problem and i was wondering if you coulde help
me. I'll try to describe it as in depth as i can.

I have a FUNCTION in a postgresql database which subtracts two DOUBLE
PRECISION FIELDS and returns the result. The problem is that when the result
should be zero, the number i
get is a number ridiculously close to zero in scientific notation (for
example 2.4697823124E-14) but not zero. I know (or at least i think i know)
the problem lies within the way postgresql and Java communicate because if a
connect through a console to the db and run the function i get the result
right (zero) but if i debug the java code i get ther wrong
non-zero-but-very-close result

this is the function:

CREATE OR REPLACE FUNCTION getSaldoParticipante(BIGINT) RETURNS DOUBLE
PRECISION AS '
DECLARE
idParticipante ALIAS FOR $1;
result DOUBLE PRECISION;
BEGIN

result := 0;

Select (Select CASE WHEN saldo ISNULL then 0 else saldo end FROM (Select
sum(PG.saldo) as saldo FROM pagos.pagos PG WHERE PG.saldo > 0 AND
PG.participante=idParticipante AND PG.deleted = false) tmp)-(Select CASE
WHEN saldo ISNULL then 0 else saldo end FROM (Select sum(DE.saldo) as saldo
FROM pagos.deudas DE WHERE DE.deleted = false AND
DE.participante=idParticipante) tmp) INTO result;

RETURN result;

END;'
LANGUAGE 'plpgsql' CALLED ON NULL INPUT;

this is the Java code where i get the result that should be zero but instead
is just very close to zero

String query = "select getSaldoParticipante(?)";
params.add(new ParameterValue(idParticipante, Types.BIGINT));

try {
conn = tx.getConnection();

//preparo y ejecuto el statement
pstmt = prepareStatement (conn, query, params);
rs = pstmt.executeQuery();

//itero los registros
while (rs.next()) {
//the problems appears at the following line
result = rs.getDouble("getSaldoParticipante");
}
}
catch(Exception e){
...


the only thing that works here is to use rs.getInt instead of rs.getDouble,
but that is not good enough since i dont want to truncate the decimal part
of the number.

So, a lot of thanks in advance, any help will be greatly appreciated.

¡Saludos!

Rafael

Rafael Barrera Oro wrote:
> Hello, i have the following problem and i was wondering if you coulde help
> me. I'll try to describe it as in depth as i can.
>
> I have a FUNCTION in a postgresql database which subtracts two DOUBLE
> PRECISION FIELDS and returns the result. The problem is that when the result
> should be zero, the number i
> get is a number ridiculously close to zero in scientific notation (for
> example 2.4697823124E-14) but not zero.

Start here:

http://www.google.com/search?q=floating+point+rounding

The short answer is - never expect the subtraction of two "equal"
floating point values to be zero. Instead of testing with equality, test
with a very small range.

If you really need exact values (say, you're working with money) use the
NUMERIC type instead.

--
Craig Ringer

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