Re: DATE_PART('field', INTERVAL) not intuitive literal reading ofinterval

On Tue, Jun 19, 2018 at 11:58:39PM -0400, Bruce Momjian wrote:
> On Tue, May 22, 2018 at 10:55:14AM +0000, PG Doc comments form wrote:
> > https://stackoverflow.com/questions/50465632/postgresql-10-4-date-difference/50465676#50465676
> 
> This is really a function of how interval computes months, days, and
> seconds from subtraction, which is outlined here:
> 
>     https://www.postgresql.org/docs/10/static/datatype-datetime.html#DATATYPE-INTERVAL-INPUT
> 
> I don't think adding something to the functions-datetime.html section
> makes sense.  For example, this returns 1:
> 
>     SELECT extract(minutes from '1 hour 1 minute'::interval);
>      date_part
>     -----------
>              1

Thinking some more, I wonder if this behavior should be more clearly
documented:

    SELECT EXTRACT(hours from '80 minutes'::interval);
     date_part
    -----------
             1
    
    SELECT EXTRACT(days from '80 hours'::interval);
     date_part
    -----------
             0

To me, this clearly shows the behavior of the months, days, and seconds
components.  I have developed the attached doc patch to mention this.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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