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

On Mon, Jul 8, 2024 at 01:03:28PM -0400, Tom Lane wrote:
> I took another look at this issue and got annoyed by the fact that the
> proposed coding for "quarter" still doesn't satisfy the rule that
> the output for a negative interval should be the negative of the
> output for the sign-reversed interval. Specifically, if the month
> field is zero, the v2 patch always emits 1:
>
> regression=# select extract(quarter from interval '1 day');
> extract
> ---------
> 1
> (1 row)
>
> regression=# select extract(quarter from interval '-1 day');
> extract
> ---------
> 1
> (1 row)
>
> We could fix that by examining the sign of the lower-order fields
> when month is zero, as in the v3 patch attached. However, I'm not
> at all sure this is really better than v2. Notably, it makes the
> documentation's statement that the result is "the month field
> divided by 3 plus 1" even more incomplete. I still don't really
> want to go into details about the behavior for negative intervals.
> OTOH if we did do that, I'd rather write a blanket statement
> about the result being the negative of the result for a positive
> interval.
>
> Thoughts?

I tested master, patch version 2 and patch version 3 with some sample
extract() queires, attached. I like patch version 2. Patch version 3
bothers me because "-600 days" is ignored if months is non-zero, and
used for its sign for zero month values, which seems odd to me; better
to ignore it.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

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