Re: Have I found an interval arithmetic bug?

On Wed, 28 Jul 2021 at 00:08, John W Higgins <wishdev(at)gmail(dot)com> wrote:
>
> It's nice to envision all forms of fancy calculations. But the fact is that
>
> '1.5 month'::interval * 2 != '3 month"::interval
>

That's not exactly true. Even without the patch:

SELECT '1.5 month'::interval * 2 AS product,
'3 month'::interval AS expected,
justify_interval('1.5 month'::interval * 2) AS justified_product,
'1.5 month'::interval * 2 = '3 month'::interval AS equal;

product | expected | justified_product | equal
----------------+----------+-------------------+-------
2 mons 30 days | 3 mons | 3 mons | t
(1 row)

So it's equal even without calling justify_interval() on the result.

FWIW, I remain of the opinion that the interval literal code should
just spill down to lower units in all cases, just like the
multiplication and division code, so that the results are consistent
(barring floating point rounding errors) and explainable.

Regards,
Dean