From: Tom Lane <tgl@sss.pgh.pa.us>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: kamiya33hirokazu@gmail.com
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: Explanation of the ROUND function with NUMERIC as an argument
Date: Sat, 03 Dec 2022 09:19:40 -0500
Message-ID: <2241115.1670077180@sss.pgh.pa.us> (raw)
In-Reply-To: <3da3dcc06220f80537dc1fb2c32cb76c91f87b93.camel@cybertec.at>
References: <167005767233.1899.2490889277144246641@wrigleys.postgresql.org>
<3da3dcc06220f80537dc1fb2c32cb76c91f87b93.camel@cybertec.at>
Laurenz Albe <laurenz.albe@cybertec.at> writes:
> On Sat, 2022-12-03 at 08:54 +0000, PG Doc comments form wrote:
>> I am thinking that the value of the ROUND function with NUMERIC as an
>> argument is rounded off, not rounded away from zero.
> It is rounded away from zero, since 43 is farther away from 0 than 42.5.
> This may be a language problem.
Perhaps, since I don't see anything wrong with that text either.
(Of course, it's moderately likely that I wrote that text,
or at least copy-edited it at some point ;-). Don't remember.)
The point is that for 42.5, or anything-point-5, the basic
"round to nearest integer" rule is insufficient because 42 and
43 are equally near. We need a tie-breaking rule, and for numeric
that rule has historically been to round to the larger absolute
value (or "away from zero", as the text puts it to avoid two-dollar
terminology). Sadly, that is not what IEEE has established as
best practice for floating-point rounding, so round(float8)
acts differently.
regards, tom lane
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To: pgsql-docs@postgresql.org
Cc: tgl@sss.pgh.pa.us, laurenz.albe@cybertec.at, kamiya33hirokazu@gmail.com, pgsql-docs@lists.postgresql.org
Subject: Re: Explanation of the ROUND function with NUMERIC as an argument
In-Reply-To: <2241115.1670077180@sss.pgh.pa.us>
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