Re: [SQL] Interval subtracting

Mark Dilger <pgsql@markdilger.com> writes:
> Tom Lane wrote:
>> The problem is that you can't determine "what answer justify_days would
>> give" without using the assumption "1 month == 30 days", which is an
>> assumption that justify_hours must not depend on.

> Ahhh.  So the fact that justify_days already makes the 1 month == 30 days 
> assumption is ok in that function but can't be propagated to justify_hours.

Right.  I don't want us to define things so that none of this
functionality is available in situations where the 30-day assumption is
untenable.  justify_hours can still do something useful (ie, trim
oversize hours fields) without that.

justify_interval will probably be the new "normal" way to do things when
you are prepared to make both assumptions.  I'm not entirely sure about
the use-case for justify_days, but seems we ought to keep it for reasons
of backwards compatibility.
        regards, tom lane