Re: BUG #18348: Inconsistency with EXTRACT([field] from INTERVAL);

I wrote:
> jian he <jian.universality@gmail.com> writes:
>> On Sun, Feb 18, 2024 at 2:14 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> (Parenthetically, one case that perhaps is surprising is
>>> ERROR:  unit "week" not supported for type interval
>>> Why not just return the day field divided by 7?)

>> seems pretty simple?

> Hm, maybe, but does this behave desirably for zero or negative days?

>> So in section 9.9.1. EXTRACT, date_part
>> we may need to document extract(quarter from interval) case.
>> intervals can be negative, which will make the issue more complicated.
>> except the "quarter" field , EXTRACT other fields from intervals, the
>> output seems sane.

> Yeah, I see what you mean: the output for negative month counts is
> very bizarre, whereas other fields seem to all produce the negative
> of what they'd produce for the absolute value of the interval.
> We could either try to fix that or decide that rejecting "quarter"
> for intervals is the saner answer.

After fooling with these cases for a little I'm inclined to think
we should do it as attached (no test or docs changes yet).

			regards, tom lane