From: Tom Lane <tgl@sss.pgh.pa.us>
To: Nuno Sousa <nunofgs@gmail.com>
cc: pgsql-novice@lists.postgresql.org
Subject: Re: Numeric Scale Differences
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Comments: In-reply-to Nuno Sousa <nunofgs@gmail.com>
	message dated "Thu, 21 Oct 2021 14:47:48 +0100"
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Date: Thu, 21 Oct 2021 10:06:04 -0400
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Nuno Sousa <nunofgs@gmail.com> writes:
> I've run into an interesting issue when trying to do numeric math. I
> expected the following to return the same number of decimal digits in the
> fractional part:

> select scale(1/0.6::numeric), scale(1/6::numeric);

Um ... why did you expect that?  The inputs to the divisions have
different scales:

# select scale(0.6::numeric), scale(6::numeric);
 scale | scale 
-------+-------
     1 |     0
(1 row)

so I find it unsurprising that the outputs do too.  Now the fact
that the output scales differ by 4 not 1 is indeed an implementation
artifact.  It stems from the numeric type working with base-10000
digits, so that scales that are multiples of 4 are most efficient,
hence division will always choose such an output scale.

			regards, tom lane