Date: Mon, 12 Apr 2021 20:25:58 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Bryn Llewellyn <bryn@yugabyte.com>
Cc: Tom Lane PostgreSQL <tgl@sss.pgh.pa.us>, Zhihong Yu <zyu@yugabyte.com>,
	Justin Pryzby <pryzby@telsasoft.com>,
	Isaac Morland <isaac.morland@gmail.com>,
	John W Higgins <wishdev@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Have I found an interval arithmetic bug?
Message-ID: <20210413002558.GC4231@momjian.us>
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On Mon, Apr 12, 2021 at 05:20:43PM -0700, Bryn Llewellyn wrote:
> I’d argue that the fact that this:
>
> ('0.3 months'::interval) + ('0.7 months'::interval)
>
> Is reported as '30 days' and not '1 month' is yet another
> bug—precisely because of what I said in my previous email (sorry
> that I forked the thread) where I referred to the fact that, in the
> right test, adding 1 month gets a different answer than adding 30
> days. 

Flowing _up_ is what these functions do:

	\df *justify*
	                               List of functions
	   Schema   |       Name       | Result data type | Argument data types | Type
	------------+------------------+------------------+---------------------+------
	 pg_catalog | justify_days     | interval         | interval            | func
	 pg_catalog | justify_hours    | interval         | interval            | func
	 pg_catalog | justify_interval | interval         | interval            | func

> Yet another convincing reason to get rid of this flow down
> business altogether.

We can certainly get rid of all downflow, which in the current patch is
only when fractional internal units are specified.

> If some application wants to model flow-down, then it can do so with
> trivial programming and full control over its own definition of the
> rules.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.