Re: BUG #14632: Plus and minus operators inconsistency with leap years and year intervals.

> On Thu, Apr 27, 2017 at 1:01 AM, Pietro Pugni <pietro(dot)pugni(at)gmail(dot)com <mailto:pietro(dot)pugni(at)gmail(dot)com>> wrote:
>> Expect 1912-02-28 is a correct response. The only reason you think the 29th comes into play here is because you remember that the starting point was the 29th. The system has no such memory.
>
> And this is logically wrong because it leads to wrong results. I’m aware that time intervals are difficult to manage but more exactness is needed here: '10 years' must have the same meaning when added to a date and subtracted from it, otherwise it leads to wrong results.
>
> Your suggestion just moves the wrong results to another use case; see my response upthread. There is no objectively correct answer here, like you seem to think.

I just found this query clearly shows the underlying algorithm is somewhat wrong:

(I)
postgres=# select age('2017-01-30'::date, '1912-02-29'::date) + '1912-02-29'::date;
?column?
---------------------
2017-01-30 00:00:00

(II)
postgres=# select age('2017-02-01'::date, '1912-02-29'::date) + '1912-02-29'::date;
?column?
---------------------
2017-01-30 00:00:00

Query (II) should return 2017-02-01 instead of 2017-01-30 and the two queries should return different results.
More generally, if we calculate the previous query on all the dates of February:

select age('2017-01-31'::date, '1912-02-29'::date) + '1912-02-29'::date;
select age('2017-02-01'::date, '1912-02-29'::date) + '1912-02-29'::date;
select age('2017-02-02'::date, '1912-02-29'::date) + '1912-02-29'::date;
select age('2017-02-03'::date, '1912-02-29'::date) + '1912-02-29'::date;
...
select age('2017-02-28'::date, '1912-02-29'::date) + '1912-02-29'::date;
select age('2017-03-01'::date, '1912-02-29'::date) + '1912-02-29'::date;

they return, respectively:
2017-01-31 00:00:00
2017-01-30 00:00:00
2017-01-31 00:00:00
2017-02-01 00:00:00
...
2017-02-26 00:00:00
2017-03-01 00:00:00

while the expected results are:
2017-01-31 00:00:00
2017-02-01 00:00:00
2017-02-02 00:00:00
2017-02-03 00:00:00
...
2017-02-28 00:00:00
2017-03-01 00:00:00

I understand why this happens (this has been discussed previously) but clearly there’s something wrong..

Kind regards
Pietro Pugni