From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Mark Dilger <pgsql@markdilger.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: [SQL] Interval subtracting
Date: Wed, 01 Mar 2006 15:28:11 -0500
Message-ID: <14834.1141244891@sss.pgh.pa.us> (raw)
In-Reply-To: <200603012013.k21KDFM21139@candle.pha.pa.us>
References: <200603012013.k21KDFM21139@candle.pha.pa.us>
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I don't think we can accept a change that takes a negative and turns it
> into a positive and negative.
Yeah, I find the patch's changes to the regression results pretty
disturbing.
Perhaps the correct definition ought to be like "if month part >= 0
then the reduced day part should be between 0 and 30, otherwise the
reduced day part should be between 0 and -30". However there are
still corner cases to worry about. If the original month and day
parts are of different sign, you might not be able to do such a
reduction without changing the sign of the month part, consider
"1 month -95 days". Not clear what to do with this.
I guess I would expect a good result to satisfy one of these three
cases:
* month > 0 and 0 <= day < 30
* month < 0 and -30 < day <= 0
* month = 0 and -30 < day < 30
If you believe that then "1 month -95 days" should justify to
"-2 months -5 days".
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgman@candle.pha.pa.us, pgsql@markdilger.com, pgsql-hackers@postgresql.org
Subject: Re: [SQL] Interval subtracting
In-Reply-To: <14834.1141244891@sss.pgh.pa.us>
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