Aggregate Overlapping Segments to Measure Effective Length

Question

I have a road_events table:

create table road_events (
    event_id number(4,0),
    road_id number(4,0),
    year number(4,0),
    from_meas number         


        

Answer 1

There is another way to calculate this, with from and to values:

with 
  part_begin_point as (
    Select distinct road_id, from_meas point
    from road_events be
    union 
    Select distinct road_id, to_meas point
    from road_events ee
  )
, newest_part as (
  select e.event_id
  , e.road_id
  , e.year
  , e.total_road_length
  , p.point
  , LAG(e.event_id) over (partition by p.road_id order by p.point) prev_event
  , e.to_meas event_to_meas
  from part_begin_point p
  join road_events e
   on p.road_id = e.road_id
   and p.point >= e.from_meas and  p.point < e.to_meas
   and not exists(
        select 1 from road_events ne 
        where e.road_id = ne.road_id
        and p.point >= ne.from_meas and p.point < ne.to_meas
        and (e.year < ne.year or e.year = ne.year and e.event_id < ne.event_id))
  )
select event_id, road_id, year
, point from_meas
, LEAD(point, 1, event_to_meas) over (partition by road_id order by point) to_meas
, total_road_length
, LEAD(point, 1, event_to_meas) over (partition by road_id order by point) - point EVENT_LENGTH
from newest_part
where 1=1
and event_id <> prev_event or prev_event is null
order by event_id, point

SQL Fiddle