Re: [BUGS] BUG #1993: Adding/subtracting negative time intervals

[ bugs list removed, hackers added.]

Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > I saw a lot of disussion because I forgot to specify that my tests were
> > for EST5EDT, but what about the use of interval_justify_hours() in
> > timestamp_mi(). Is this something we want to change?
>
> It's too late to mess with it for 8.1, but see my previous message
> proposing a set of TODO items for future work.

Yes, it is late, but I am worried about adding an interface change that
we will later revert in 8.2. In 8.0.X I see the query returning the '25
hour' answer:

SELECT
('2005-10-29 13:22:00-04'::timestamptz +
('2005-10-30 13:22:00-05'::timestamptz -
'2005-10-29 13:22:00-04'::timestamptz)) at time zone 'EST';

timezone
---------------------
2005-10-30 13:22:00
(1 row)

In current CVS the top query returns '14:22:00'. Do we change this for
8.1, then change it back in 8.2? That seems bad to me.

Actually, 8.0.X returns '1 day, 1 hour' for the subtraction, which we
treat in 8.0.X as '25 hours':

SELECT
('2005-10-30 13:22:00-05'::timestamptz -
'2005-10-29 13:22:00-04'::timestamptz);

?column?
----------------
1 day 01:00:00
(1 row)

In 8.0.X, because we didn't have a 'days' field, we could treat '1 day 1
hour' as always '25 hours', and could display the results as days/hours.
If we remove interval_justify_hours(), then we are always going to
display timestamp subtraction in hours (not days), e.g. '6422 hours'
(yea, ugly) unless they manually call interval_justify_hours().

Keep in mind that the addition of the interval_justify_hours() did
generate some regression test changes, so removing
interval_justify_hours() might just take the results back to what we had
in 8.0. My point is that regression changes caused by its removal might
not be a good guide to determining compatibility with 8.0.X.

I guess my point is that we are changing 8.0.X behavior so we better be
sure it is now the way we want it to remain.

--
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