Re: [SQL] Interval subtracting

Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)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

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