Date: Wed, 1 Mar 2006 12:32:42 -0800 (PST)
From: Stephan Szabo <sszabo@megazone.bigpanda.com>
To: Hannu Krosing <hannu@skype.net>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
	Tom Lane <tgl@sss.pgh.pa.us>, "Milen A. Radev" <milen@radev.net>,
	pgsql-sql@postgresql.org, pgsql-hackers@postgresql.org
Subject: Re: [SQL] Interval subtracting
In-Reply-To: <1141244920.3737.10.camel@localhost.localdomain>
Message-ID: <20060301123127.D11836@megazone.bigpanda.com>
References: <200603012018.k21KIhi22006@candle.pha.pa.us>
	<1141244920.3737.10.camel@localhost.localdomain>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=utf-8
Content-Transfer-Encoding: QUOTED-PRINTABLE

On Wed, 1 Mar 2006, Hannu Krosing wrote:

> =C3=9Chel kenal p=C3=A4eval, K, 2006-03-01 kell 15:18, kirjutas Bruce Mom=
jian:
> > 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 >=3D 3=
0 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 <=3D days < 30, not merely days < 30.
> > >
> > > What about cases like interval '1 month -99 days', should that turn i=
nto
> > > 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:
> >
> > =09'2 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'.

Right, but would you call justify_days on such an interval?  '2 months -1
days' <> '1 mon 29 days', but '1 mon 60 days' is also <> '3 mons' in
general usage.