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

jian he <jian(dot)universality(at)gmail(dot)com> writes:
> On Wed, Feb 21, 2024 at 4:56 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> 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).

> ... I don't know how to write the documentation for the `quarter` when
> it's negative.

After poking at it some more, I realized that my draft patch was still
wrong about that. We really have to look at interval->month if we
want to behave plausibly for negative months.

Here's a more fleshed-out patch. I don't think we really need to
document the behavior for negative intervals; at least, we haven't
done that so far for any other fields. I did add testing of such
cases though.

regards, tom lane