Subject: Re: [SQL] Interval subtracting
From: Hannu Krosing <hannu@skype.net>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Stephan Szabo <sszabo@megazone.bigpanda.com>,
	Tom Lane <tgl@sss.pgh.pa.us>, "Milen A. Radev" <milen@radev.net>,
	pgsql-sql@postgresql.org, pgsql-hackers@postgresql.org
In-Reply-To: <200603012018.k21KIhi22006@candle.pha.pa.us>
References: <200603012018.k21KIhi22006@candle.pha.pa.us>
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Date: Wed, 01 Mar 2006 22:28:39 +0200
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Ühel kenal päeval, K, 2006-03-01 kell 15:18, kirjutas Bruce Momjian:
> Stephan Szabo wrote:
> > > justify_days doesn't currently do anything with this result --- it
> > > thinks its charter is only to reduce day components that are >= 30 days.
> > > However, I think a good case could be made that it should normalize
> > > negative days too; that is, the invariant on its result should be
> > > 0 <= days < 30, not merely days < 30.
> > 
> > What about cases like interval '1 month -99 days', should that turn into
> > interval '-3 mons +21 days' or '-2 mons -9 days'?
> 
> I think it should be the later.  It is best to have a single sign, and I
> think it is possible in all cases:
> 
> 	'2 mons -1 days'
> 
> could be adjusted to '1 mons 29 days'.

But unfortunately '2 mons -1 days' <> '1 mons 29 days'

If I want something to happen 1 day less than two months from dome date,
then the only way to say that consistently *is* '2 mons -1 days'.

--------------
Hannu