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

Thought about this too much today, but I have something that ignores the +/- 10 meters now.

First made a function that takes in to / from pairs as a string and returns the distance covered by the pairs in the string. For example '10:20;35:45' returns 20.

CREATE
    OR replace FUNCTION get_distance_range_str (strRangeStr VARCHAR2)

RETURN NUMBER IS intRetNum NUMBER;

BEGIN
    --split input string
    WITH cte_1
    AS (
        SELECT regexp_substr(strRangeStr, '[^;]+', 1, LEVEL) AS TO_FROM_STRING
        FROM dual connect BY regexp_substr(strRangeStr, '[^;]+', 1, LEVEL) IS NOT NULL
        )
        --split From/To pairs
        ,cte_2
    AS (
        SELECT cte_1.TO_FROM_STRING
            ,to_number(substr(cte_1.TO_FROM_STRING, 1, instr(cte_1.TO_FROM_STRING, ':') - 1)) AS FROM_MEAS
            ,to_number(substr(cte_1.TO_FROM_STRING, instr(cte_1.TO_FROM_STRING, ':') + 1, length(cte_1.TO_FROM_STRING) - instr(cte_1.TO_FROM_STRING, ':'))) AS TO_MEAS
        FROM cte_1
        )
        --merge ranges
        ,cte_merge_ranges
    AS (
        SELECT s1.FROM_MEAS
            ,
            --t1.TO_MEAS 
            MIN(t1.TO_MEAS) AS TO_MEAS
        FROM cte_2 s1
        INNER JOIN cte_2 t1 ON s1.FROM_MEAS <= t1.TO_MEAS
            AND NOT EXISTS (
                SELECT *
                FROM cte_2 t2
                WHERE t1.TO_MEAS >= t2.FROM_MEAS
                    AND t1.TO_MEAS < t2.TO_MEAS
                )
        WHERE NOT EXISTS (
                SELECT *
                FROM cte_2 s2
                WHERE s1.FROM_MEAS > s2.FROM_MEAS
                    AND s1.FROM_MEAS <= s2.TO_MEAS
                )
        GROUP BY s1.FROM_MEAS
        )
    SELECT sum(TO_MEAS - FROM_MEAS) AS DISTANCE_COVERED
    INTO intRetNum
    FROM cte_merge_ranges;

    RETURN intRetNum;
END;

Then wrote this query that builds a string for that function for the appropriate prior range. Couldn't use windowing with list_agg, but was able to achieve same with a correlated subquery.

--use list agg to create list of to/from pairs for rows before current row in the ordering
WITH cte_2
AS (
    SELECT T1.*
        ,(
            SELECT LISTAGG(FROM_MEAS || ':' || TO_MEAS || ';') WITHIN
            GROUP (
                    ORDER BY ORDER BY YEAR DESC, EVENT_ID DESC
                    )
            FROM road_events T2
            WHERE T1.YEAR || lpad(T1.EVENT_ID, 10,'0') < 
                T2.YEAR || lpad(T2.EVENT_ID, 10,'0')
                AND T1.ROAD_ID = T2.ROAD_ID
            GROUP BY road_id
            ) AS PRIOR_RANGES_STR
    FROM road_events T1
    )
    --get distance for prior range string - distance ignoring current row
    --get distance including current row
    ,cte_3
AS (
    SELECT cte_2.*
        ,coalesce(get_distance_range_str(PRIOR_RANGES_STR), 0) AS DIST_PRIOR
        ,get_distance_range_str(PRIOR_RANGES_STR || FROM_MEAS || ':' || TO_MEAS || ';') AS DIST_NOW
    FROM cte_2 cte_2
    )
    --distance including current row less distance ignoring current row is distance added to the range this row
    ,cte_4
AS (
    SELECT cte_3.*
        ,DIST_NOW - DIST_PRIOR AS DIST_ADDED_THIS_ROW
    FROM cte_3
    )
SELECT *
FROM cte_4
--filter out any rows with distance added as 0
WHERE DIST_ADDED_THIS_ROW > 0
ORDER BY ROAD_ID, YEAR DESC, EVENT_ID DESC

sqlfiddle here: http://sqlfiddle.com/#!4/81331/36

Looks to me like the results match yours. I left the additional columns in the final query to try to illustrate each step.

Works on the test case - might need some work to handle all possibilities in a larger data set, but I think this would be a good place to start and refine.

Credit for Overlapping range merge is first answer here: Merge overlapping date intervals

Credit for list_agg with windowing is first answer here: LISTAGG equivalent with windowing clause