Re: [SQL] Interval subtracting

Mark Dilger wrote:
> Tom Lane wrote:
> > Well, the question is whether justify_days has a sane definition that is
> > different from this. Based on your example, I'm not seeing one.
>
> Backwards compatibility is probably more important than sanity. Let's just
> deprecate the existing functions and recommend that people use
> justify_interval(...). By not changing the existing functions we can avoid a
> certain amount of hell.

Those functions are new in 8.1 so I do think we can improve them in 8.2
if we agree. Tom's idea of:

> * month > 0 and 0 <= day < 30
> * month < 0 and -30 < day <= 0
> * month = 0 and -30 < day < 30

seems a good change for 8.2, and the same for justify_hours(). The
question is whether justify_days should also adjust hours I think is the
issue, and the reason for a justify_interval() function. Even if we had
people do:

justify_hours(justify_days(justify_hours()))

I don't think that would do what we want in all cases. Consider '1 mon
-1 hour'. That should be '29 days 23 hours' but neither existing
function, even if modified, will allow us to return that. Only
something like justify_interval() could do it.

--
Bruce Momjian http://candle.pha.pa.us
SRA OSS, Inc. http://www.sraoss.com

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