Re: [SQL] Interval subtracting

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Milen A(dot) Radev" <milen(at)radev(dot)net>, pgsql-sql(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org
Subject: Re: [SQL] Interval subtracting
Date: 2006-03-01 20:18:43
Message-ID: 200603012018.k21KIhi22006@candle.pha.pa.us
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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'.

--
Bruce Momjian http://candle.pha.pa.us
SRA OSS, Inc. http://www.sraoss.com

+ If your life is a hard drive, Christ can be your backup. +

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