From: Tom Lane <tgl@sss.pgh.pa.us>
To: Erik Brandsberg <erik@heimdalldata.com>
cc: szy <598546998@qq.com>, pgsql-sql <pgsql-sql@lists.postgresql.org>
Subject: Re: Inconsistent results for division and multiplication operations
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Comments: In-reply-to Erik Brandsberg <erik@heimdalldata.com>
	message dated "Mon, 25 Nov 2024 10:53:38 -0500"
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Date: Mon, 25 Nov 2024 11:34:38 -0500
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Erik Brandsberg <erik@heimdalldata.com> writes:
> This is a common issue with using floating point math.  You will see the
> same issue with many systems.  Basically, the order of operations can
> trigger very minor differences in results, but if you round the first
> result to the same number of significant digits as the input, it would b=
e
> identical.
> https://learn.microsoft.com/en-us/office/troubleshoot/access/floating-ca=
lculations-info

Yeah.  The OP is actually working with PG's "numeric" type, not
floating-point, but the principle is the same.  Some division
results can't be represented exactly in any finite number of
digits, so you get roundoff error.

			regards, tom lane