On Wed, 28 Jul 2021 at 00:08, John W Higgins <wishdev@gmail.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)
That's viewing something via the mechanism that is incorrectly (technically speaking) doing the work in the first place. It believes they are the same - but they are clearly not when actually used.
That's the flaw in this entire body of work - we keep taking fractional amounts - doing round offs and then trying to add or multiply the pieces back and ending up with weird floating point math style errors. That's never to complain about it - but we shouldn't be looking at edge cases with things like 1 month * 1.234 when 1.5 months * 2 doesn't work properly.
