On 03/06/2013 07:16 PM, François Beausoleil wrote:
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 rounding the result. Sometimes that result is negative and rounding it returns (or shows up as) a negative zero (-0) in a SELECT.
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 754 and 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
This is happening in a plpgsql function, so I guess that makes it C,
under the hood. That does help, thank you.
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