Re: BUG #14850: Implement optinal additinal parameter for 'justify' date/time function

On Wed, Oct 11, 2017 at 10:35:12AM +0000, kes-kes(at)yandex(dot)ru wrote:
>
> >Adjust interval so 30-day time periods are represented as months
>
> https://www.postgresql.org/docs/9.6/static/functions-datetime.html
>

Yes, it seems that it is because timestamp operations return '29 days':

=# SELECT timestamp '2016-01-31' +interval '1 month' -timestamp '2016-01-31';
?column?
----------
29 days

You can also try the following, maybe it is appropriate for you:

=# SELECT timestamp '2016-01-31' -timestamp '2016-01-31' +interval '1 month';
?column?
----------
1 mon

=# SELECT extract( month from justify_days( timestamp '2016-01-31'
-timestamp '2016-01-31' +interval '1 month') );
date_part
-----------
1

--
Arthur Zakirov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company