问如何根据PostgreSQL中的枚举列总结所有行？

EN

select distinct on (floor(timeindex)::int) 
    floor(timeindex)::int idx, timeindex, timeelapse
from mytable
where fnname = 'ff'
and timetype = 'Lap'
order by 1, 2 desc;

 idx | timeindex | timeelapse 
-----+-----------+------------
   1 |       1.1 | 01:00:00
   2 |       2.3 | 03:00:00
   3 |       3.3 | 08:00:00
(3 rows)

select sum(timeelapse) from (
    select distinct on (floor(timeindex)::int) 
        floor(timeindex)::int idx, timeindex, timeelapse
    from mytable
    where fnname = 'ff'
    and timetype = 'Lap'
    order by 1, 2 desc
    ) alias;

   sum    
----------
 12:00:00
(1 row)