From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200603012302.k21N2Hm04879@candle.pha.pa.us>
Subject: Re: [SQL] Interval subtracting
In-Reply-To: <16569.1141253147@sss.pgh.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 1 Mar 2006 18:02:17 -0500 (EST)
CC: Mark Dilger <pgsql@markdilger.com>, pgsql-hackers@postgresql.org
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Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Imagine this:
> 
> > 	'1 mons -2 days -12:00:00'
> 
> > Which sign do we head to for this?  For justify_hours, if we don't look
> > at the months it remains unchange, but calling justify_days we get:
> 
> > 	'28 days -12:00:00'
> 
> > which is wrong (negative and positive).
> 
> Ugh, that's not good.
> 
> Based on that, I guess I have to change my vote: justify_hours should
> still not look at the month (because it shouldn't use the month=30days
> assumption), but justify_days should be changed to be effectively a
> combination of both functions --- that is, it should fix all three
> fields using both the 30days and the 24hours assumptions.  Then it could
> guarantee that all come out with the same sign.

If we do that, we should just call it justify_interval().  I am thinking
this is the direction to go, and for people who want more control they
use the justify_hours and justify_days, and those are left unchanged.

Should justify_days() look at hours only if the day and hours signs
differ?  And perhaps only if the hours is between -24 and 0.

-- 
  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. +