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From: Tom Lane <[email protected]>
To: Nuno Sousa <[email protected]>
Cc: [email protected]
Subject: Re: Numeric Scale Differences
Date: Thu, 21 Oct 2021 10:06:04 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAMZ4ZVqq9kHN7DJs5T=zL8jDJuk-3v2-spyYtjd8e2xj_OPM8Q@mail.gmail.com>
References: <CAMZ4ZVqq9kHN7DJs5T=zL8jDJuk-3v2-spyYtjd8e2xj_OPM8Q@mail.gmail.com>

Nuno Sousa <[email protected]> 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

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