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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <bruce@momjian.us>
cc: Bryn Llewellyn <bryn@yugabyte.com>, Zhihong Yu <zyu@yugabyte.com>,
        Justin Pryzby <pryzby@telsasoft.com>,
        Isaac Morland <isaac.morland@gmail.com>,
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Subject: Re: Have I found an interval arithmetic bug?
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Comments: In-reply-to Bruce Momjian <bruce@momjian.us>
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Date: Mon, 12 Apr 2021 19:38:21 -0400
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Bruce Momjian <bruce@momjian.us> writes:
> On Mon, Apr 12, 2021 at 03:09:48PM -0700, Bryn Llewellyn wrote:
>> After all, you've bitten the bullet now and changed the behavior. This =
means that the semantics of some extant applications will change. So... in=
 for a penny, in for a pound?

> The docs now say:

>      Field values can have fractional parts;  for example, <literal>'1.5
>      weeks'</literal> or <literal>'01:02:03.45'</literal>.  The fraction=
al
> -->  parts are used to compute appropriate values for the next lower-ord=
er
>      internal fields (months, days, seconds).

> meaning fractional years flows to the next lower internal unit, months,
> and no further.  Fractional months would flow to days.  The idea of not
> flowing past the next lower-order internal field is that the
> approximations between units are not precise enough to flow accurately.

Um, what's the argument for down-converting AT ALL?  The problem is
precisely that any such conversion is mostly fictional.

> With my patch, the output is now:

> 	SELECT INTERVAL '3 years 10.241604 months';
> 	        interval
> 	------------------------
> 	 3 years 10 mons 7 days

> It used to flow to seconds.

Yeah, that's better than before, but I don't see any principled argument
for it not to be "3 years 10 months", full stop.

			regards, tom lane