如何确定间隔的最大分辨率？

justify_interval()

test=# select justify_interval(INTERVAL \'100 days 3 seconds\');
    justify_interval     
-------------------------
 3 mons 10 days 00:00:03
(1 row)

test=# select justify_interval(TIME \'20:05\' - TIME \'12:01:01\');
 justify_interval 
------------------
 08:03:59
(1 row)

test=# select justify_interval(AGE(NOW(), NOW() - INTERVAL \'1 MONTH\'));
 justify_interval 
------------------
 1 mon
(1 row)

test=# select extract(\'mon\' from interval \'3 mons 10 days 00:00:03\');
 date_part 
-----------
         3

create function max_res(interval) returns interval as $$
select case
       when extract(\'year\' from justify_interval($1)) > 0 or
            extract(\'mon\' from justify_interval($1)) > 0 or
            extract(\'day\' from justify_interval($1)) > 0
       then \'1 day\'
       when extract(\'hour\' from justify_interval($1)) > 0
       then \'1 hour\'
       when ...
       end;
$$ language sql immutable strict;

year

1 month

tm_mon

struct tm

INTERVAL

t := EXTRACT(EPOCH FROM my_time_input);
IF t >= 31104000 THEN
  RETURN \'year\';
ELSIF t >= 2592000 THEN
  RETURN \'month\';
ELSIF t >= 604800 THEN
  RETURN \'week\';
ELSIF t >= 86400 THEN
  RETURN \'day\';
ELSIF t >= 3600 THEN
  RETURN \'hour\';
ELSIF t >= 60 THEN
  RETURN \'minute\'
ELSIF t > 1 THEN
  RETURN \'seconds\';
ELSIF t == 1 THEN
  RETURN \'second\';
ELSE
  RETURN resolve_largest_sub_second_unit(my_time);
END IF;