Re: truncating timestamps on arbitrary intervals

Hello,

On 3/13/2020 4:13 PM, John Naylor wrote:
> I've put off adding documentation on the origin piece pending comments
> about the approach.
> 
> I haven't thought seriously about timezone yet, but hopefully it's
> just work and nothing to think too hard about.

Thank you for the patch. I looked it and tested a bit.

There is one interesting case which might be mentioned in the 
documentation or in the tests is the following. The function has 
interesting behaviour with real numbers:

=# select date_trunc_interval('0.1 year'::interval, TIMESTAMP 
'2020-02-01 01:21:01');
  date_trunc_interval
---------------------
  2020-02-01 00:00:00

=# select date_trunc_interval('1.1 year'::interval, TIMESTAMP 
'2020-02-01 01:21:01');
ERROR:  only one interval unit allowed for truncation

It is because the second interval has two interval units:

=# select '0.1 year'::interval;
  interval
----------
  1 mon

=# select '1.1 year'::interval;
    interval
--------------
  1 year 1 mon

-- 
Artur