From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | "mirek" <mirek(at)mascort(dot)com(dot)pl> |
Cc: | pgsql-bugs(at)postgresql(dot)org |
Subject: | Re: BUG #3991: pgsql function sum() |
Date: | 2008-02-26 15:45:08 |
Message-ID: | 2945.1204040708@sss.pgh.pa.us |
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Lists: | pgsql-bugs |
"mirek" <mirek(at)mascort(dot)com(dot)pl> writes:
> problem is in: sum(wvat-wvatp) where field in view wvat = 33.08 and wvatp =
> 36.09
> Result is -3.01000000000001
> If I ask postgres manualy: select sum(33.08 - 36.09)
> result is ok -3.01
> Now I fix it with round function but i think that is a bug.
You evidently haven't got much experience with working with
floating-point arithmetic.
regression=# select 33.08::numeric - 36.09::numeric;
?column?
----------
-3.01
(1 row)
regression=# select 33.08::float8 - 36.09::float8;
?column?
-------------------
-3.01000000000001
(1 row)
This is not a bug, it's an inherent consequence of the fact that these
decimal values are not exactly represented in a binary floating-point
system. If you don't like it, don't use float.
regards, tom lane
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