Re: [SQL] Interval subtracting

Tom Lane wrote:
> Mark Dilger <pgsql(at)markdilger(dot)com> writes:
>
>>Tom Lane wrote:
>>
>>>If so, one function or the other is cheating.
>
>
>>That depends what you mean by cheating. The justify_hours function
>>looks to see what answer justify_days would give, but does not
>>actually change the data. I described this all earlier and I still
>>don't see why there is anything wrong with it.
>
>
> 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.