Обединяване на припокриващи се сегменти за измерване на ефективната дължина

Моята основна СУБД е Teradata, но това ще работи както е и в Oracle.

WITH all_meas AS
 ( -- get a distinct list of all from/to points
   SELECT road_id, from_meas AS meas
   FROM road_events
   UNION
   SELECT road_id, to_meas
   FROM road_events
 )
-- select * from all_meas order by 1,2
 , all_ranges AS
 ( -- create from/to ranges
   SELECT road_id, meas AS from_meas 
     ,Lead(meas)
      Over (PARTITION BY road_id
            ORDER BY meas) AS to_meas
   FROM all_meas
  )
 -- SELECT * from all_ranges order by 1,2
, all_event_ranges AS
 ( -- now match the ranges to the event ranges
   SELECT 
      ar.*
     ,re.event_id
     ,re.year
     ,re.total_road_length
     ,ar.to_meas - ar.from_meas AS event_length
     -- used to filter the latest event as multiple events might cover the same range 
     ,Row_Number()
      Over (PARTITION BY ar.road_id, ar.from_meas
            ORDER BY year DESC) AS rn
   FROM all_ranges ar
   JOIN road_events re
     ON ar.road_id = re.road_id
    AND ar.from_meas < re.to_meas
    AND ar.to_meas > re.from_meas
   WHERE ar.to_meas IS NOT NULL
 )
SELECT event_id, road_id, year, total_road_length, Sum(event_length)
FROM all_event_ranges
WHERE rn = 1 -- latest year only
GROUP BY event_id, road_id, year, total_road_length
ORDER BY road_id, year DESC;

Ако трябва да върнете действително покрития from/to_meas (както във вашия въпрос преди редактиране), може да е по-сложно. Първата част е същата, но без агрегиране заявката може да върне съседни редове със същия event_id (напр. за събитие 3:0-1 &1-25):

SELECT * FROM all_event_ranges
WHERE rn = 1
ORDER BY road_id, from_meas;

Ако искате да обедините съседни редове, имате нужда от още две стъпки (използвайки стандартен подход, маркирайте първия ред от група и изчислете номер на група):

WITH all_meas AS
 (
   SELECT road_id, from_meas AS meas
   FROM road_events
   UNION
   SELECT road_id, to_meas
   FROM road_events
 )
-- select * from all_meas order by 1,2
 , all_ranges AS
 ( 
   SELECT road_id, meas AS from_meas 
     ,Lead(meas)
      Over (PARTITION BY road_id
            ORDER BY meas) AS to_meas
   FROM all_meas
  )
-- SELECT * from all_ranges order by 1,2
, all_event_ranges AS
 (
   SELECT 
      ar.*
     ,re.event_id
     ,re.year
     ,re.total_road_length
     ,ar.to_meas - ar.from_meas AS event_length
     ,Row_Number()
      Over (PARTITION BY ar.road_id, ar.from_meas
            ORDER BY year DESC) AS rn
   FROM all_ranges ar
   JOIN road_events  re
     ON ar.road_id = re.road_id
    AND ar.from_meas < re.to_meas
    AND ar.to_meas > re.from_meas
   WHERE ar.to_meas IS NOT NULL
 )
-- SELECT * FROM all_event_ranges WHERE rn = 1 ORDER BY road_id, from_meas
, adjacent_events AS 
 ( -- assign 1 to the 1st row of an event
   SELECT t.*
     ,CASE WHEN Lag(event_id)
                Over(PARTITION BY road_id
                     ORDER BY from_meas) = event_id
           THEN 0 
           ELSE 1 
      END AS flag
   FROM all_event_ranges t
   WHERE rn = 1
 )
-- SELECT * FROM adjacent_events ORDER BY road_id, from_meas 
, grouped_events AS
 ( -- assign a groupnumber to adjacent rows using a Cumulative Sum over 0/1
   SELECT t.*
     ,Sum(flag)
      Over (PARTITION BY road_id
            ORDER BY from_meas
            ROWS Unbounded Preceding) AS grp
   FROM adjacent_events t
)
-- SELECT * FROM grouped_events ORDER BY  road_id, from_meas
SELECT event_id, road_id, year, Min(from_meas), Max(to_meas), total_road_length, Sum(event_length)
FROM grouped_events
GROUP BY event_id, road_id, grp, year, total_road_length
ORDER BY 2, Min(from_meas);

Редактиране:

Ups, току-що намерих блог Припокриващи се диапазони с приоритет прави точно същото с някакъв опростен синтаксис на Oracle. Всъщност преведох заявката си от някакъв друг опростен синтаксис в Teradata към Standard/Oracle SQL :-)