Le 2013-03-06 à 21:42, Tony Dare a écrit :
> I'm taking an standard deviation of a population and subtracting it from the average of the same population and
roundingthe result. Sometimes that result is negative and rounding it returns (or shows up as) a negative zero (-0) in
aSELECT.
>
> basically:
> SELECT
> client_name, avg(rpt_cnt),
> stddev_pop(rpt_cnt),
> round(avg(rpt_cnt) - stddev_pop(rpt_cnt))
> from client_counts
> group by client_name
>
> and what I sometimes get is :
> client_name | a dp number | a dp number | -0
>
> In postgresql-world, is -0 = 0? Can I use that negative 0 in further calculations without fear? Is this a bug?
This is related to the recent discussion of floating point values on this mailing list. You can read more about IEEE
754and whether 0 == -0 on Wikipedia: https://en.wikipedia.org/wiki/Signed_zero#Comparisons
According to that article, IEEE 754 specifies that 0 == -0 in Java/C/etc.
Hope that helps!
François Beausoleil