On 3/26/2010 12:12 PM, Tom Lane wrote:
Gaietti, Mauro \(SELEX GALILEO Guest,
Italy\)mauro.gaie...@guests.selexgalileo.com writes:
This query:
select round(0.5), round(0.5::integer), round(0.5::bigint), round(
0.5::float ), round( 0.5::double precision ),round(cast(0.5 as double
precision )),round(cast(0.5::double precision as numeric )); has strange
result:
1 1 1 0 0 0 1
Is this correct?
On most machines the float4/float8 operations follow the IEEE-754 spec's
round to nearest even rule for such cases. I think all the other ones
are add 0.5 and truncate implementations. It's unlikely we'll mess
with either; and *highly* unlikely that we would change the float
behavior since that's not even under our direct control (the hardware or
libm is what's doing that). There's some case to be made for making
numeric and integer math do it the IEEE way, but I think that would
displease at least as many people as it pleased ...
regards, tom lane
This topic keeps coming up every few months about rounding which way is
correct. I would be in favor of adding a option to round() function to
specify method.
Leave the defaults as they are for backwards capability, meaning if no
option is passed to Round() it follows current methods. I agree
changing how it works now would annoy many.
The option would be very simple something like this
Round( 0.5, RoundToEven) = 0
Round( -0.5, RoundToEven) = 0
Round(0.5, RoundUp) = 1
Round(-0.5, RoundUp) = 0
Round(0.5, RoundDown) = 0
Round(-0.5, RoundDown) = -1
Round(0.5, RoundToZero) = 0
Round(-0.5, RoundToZero) = 0
There are so many methods of rounding to choose from
http://en.wikipedia.org/wiki/Rounding
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