From: Bruce Momjian <bruce@momjian.us>
Message-Id: <200704022246.l32MkFI13247@momjian.us>
Subject: Re: [HACKERS] timestamp subtraction (was Re: formatting
	intervals with to_char)
In-Reply-To: <20070223162426.GI19527@nasby.net>
To: "Jim C. Nasby" <jim@nasby.net>
Date: Mon, 2 Apr 2007 18:46:15 -0400 (EDT)
CC: Jim Nasby <jimn@enterprisedb.com>, Tom Lane <tgl@sss.pgh.pa.us>,
	gdavis@refractions.net, pgsql-sql@postgresql.org,
	pgsql-hackers@postgresql.org
MIME-Version: 1.0
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Added to TODO:

        o Have timestamp subtraction not call justify_hours()?

          http://archives.postgresql.org/pgsql-sql/2006-10/msg00059.php


---------------------------------------------------------------------------

Jim C. Nasby wrote:
> Yes, but if it was '2004-01-02 01:00:00'-'2004-01-01 00:00:00' it should
> return 25:00:00, not 1 day 1:00.
> 
> I agree with Tom that this should be changed; I'm just arguing that we
> might well need a backwards-compatibility solution for a while. At the
> very least we'd need to make this change very clear to users.
> 
> On Tue, Feb 20, 2007 at 08:07:11PM -0500, Bruce Momjian wrote:
> > 
> > One problem with removing justify_hours() is that this is going to
> > return '24:00:00', rather than '1 day:
> > 	
> > 	test=> select '2004-01-02 00:00:00'::timestamptz - '2004-01-01
> > 	00:00:00'::timestamptz;
> > 	 ?column?
> > 	----------
> > 	 24:00:00
> > 	(1 row)
> > 
> > ---------------------------------------------------------------------------
> > 
> > Jim Nasby wrote:
> > > On Oct 5, 2006, at 11:50 AM, Tom Lane wrote:
> > > > regression=# select ('2006-09-15 23:59:00'::timestamp - '2006-09-01  
> > > > 09:30:41'::timestamp);
> > > >      ?column?
> > > > ------------------
> > > >  14 days 14:28:19
> > > > (1 row)
> > > >
> > > > should be reporting '350:28:19' instead.
> > > >
> > > > This is a hack that was done to minimize the changes in the regression
> > > > test expected outputs when we changed type interval from months/ 
> > > > seconds
> > > > to months/days/seconds.  But I wonder whether it wasn't a dumb idea.
> > > > It is certainly inconsistent, as noted in the code comments.
> > > >
> > > > I'm tempted to propose that we remove the justify_hours call, and tell
> > > > anyone who really wants the old results to apply justify_hours() to  
> > > > the
> > > > subtraction result for themselves.  Not sure what the fallout would  
> > > > be,
> > > > though.
> > > 
> > > I suspect there's applications out there that are relying on that  
> > > being nicely formated for display purposes.
> > > 
> > > I agree it should be removed, but we might need a form of backwards  
> > > compatibility for a version or two...
> > > --
> > > Jim Nasby                                    jimn@enterprisedb.com
> > > EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)
> > > 
> > > 
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> > -- 
> >   Bruce Momjian  <bruce@momjian.us>          http://momjian.us
> >   EnterpriseDB                               http://www.enterprisedb.com
> > 
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> -- 
> Jim Nasby                                            jim@nasby.net
> EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)
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-- 
  Bruce Momjian  <bruce@momjian.us>          http://momjian.us
  EnterpriseDB                               http://www.enterprisedb.com

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