Re: Have I found an interval arithmetic bug?

Bruce Momjian <bruce(at)momjian(dot)us> writes:
> On Mon, Apr 12, 2021 at 03:09:48PM -0700, Bryn Llewellyn wrote:
>> After all, you've bitten the bullet now and changed the behavior. This means that the semantics of some extant applications will change. So... in for a penny, in for a pound?

> The docs now say:

> Field values can have fractional parts; for example, <literal>'1.5
> weeks'</literal> or <literal>'01:02:03.45'</literal>. The fractional
> --> parts are used to compute appropriate values for the next lower-order
> internal fields (months, days, seconds).

> meaning fractional years flows to the next lower internal unit, months,
> and no further. Fractional months would flow to days. The idea of not
> flowing past the next lower-order internal field is that the
> approximations between units are not precise enough to flow accurately.

Um, what's the argument for down-converting AT ALL? The problem is
precisely that any such conversion is mostly fictional.

> With my patch, the output is now:

> SELECT INTERVAL '3 years 10.241604 months';
> interval
> ------------------------
> 3 years 10 mons 7 days

> It used to flow to seconds.

Yeah, that's better than before, but I don't see any principled argument
for it not to be "3 years 10 months", full stop.

regards, tom lane