sql - 聚合重叠段以测量有效长度

Question

我有一张road_events桌子：

create table road_events (
    event_id number(4,0),
    road_id number(4,0),
    year number(4,0),
    from_meas number(10,2),
    to_meas number(10,2),
    total_road_length number(10,2)
    );

insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (1,1,2020,25,50,100);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (2,1,2000,25,50,100);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (3,1,1980,0,25,100);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (4,1,1960,75,100,100);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (5,1,1940,1,100,100);

insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (6,2,2000,10,30,100);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (7,2,1975,30,60,100);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (8,2,1950,50,90,100);

insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (9,3,2050,40,90,100);

insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (10,4,2040,0,200,200);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (11,4,2013,0,199,200);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (12,4,2001,0,200,200);

insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (13,5,1985,50,70,300);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (14,5,1985,10,50,300);
insert into road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) values (15,5,1965,1,301,300);
commit;

select * from road_events;

---

  EVENT_ID    ROAD_ID       YEAR  FROM_MEAS    TO_MEAS TOTAL_ROAD_LENGTH
---------- ---------- ---------- ---------- ---------- -----------------
         1          1       2020         25         50               100
         2          1       2000         25         50               100
         3          1       1980          0         25               100
         4          1       1960         75        100               100
         5          1       1940          1        100               100

         6          2       2000         10         30               100
         7          2       1975         30         60               100
         8          2       1950         50         90               100

         9          3       2050         40         90               100

        10          4       2040          0        200               200
        11          4       2013          0        199               200
        12          4       2001          0        200               200

        13          5       1985         50         70               300
        14          5       1985         10         50               300
        15          5       1965          1        301               300

---

我想选择代表每条道路上最近工作的事件。

这是一个棘手的操作，因为事件通常只涉及道路的一部分。这意味着我不能简单地选择每条道路的最新事件；我只需要选择不重叠的最近事件里程。

---

可能的逻辑（按顺序）：

我不愿意猜测如何解决这个问题，因为它最终可能带来的伤害大于帮助（有点像XY 问题）。另一方面，它可能会提供对问题本质的洞察，所以这里是：

1. 为每条道路选择最近的事件。我们将调用最近的事件：event A.
2. 如果event A 是>= total_road_length，那么这就是我所需要的。算法到此结束。
3. 否则，获取与event B不具有相同范围的下一个按时间顺序排列的事件 ( ) event A。
4. 如果 的范围event B与 的范围重叠event A，则只得到event B不重叠的部分。
5. 重复步骤 3 和 4，直到总事件长度为= total_road_length。或者当该路没有更多事件时停止。

---

问题：

我知道这是一项艰巨的任务，但要做到这一点需要什么？

这是一个经典的线性参考问题。如果我可以将线性引用操作作为查询的一部分进行，那将非常有帮助。

结果将是：

  EVENT_ID    ROAD_ID       YEAR  TOTAL_ROAD_LENGTH   EVENT_LENGTH
---------- ---------- ----------  -----------------   ------------
         1          1       2020                100             25
         3          1       1980                100             25
         4          1       1960                100             25
         5          1       1940                100             25

         6          2       2000                100             20
         7          2       1975                100             30
         8          2       1950                100             30

         9          3       2050                100             50

        10          4       2040                200            200

        13          5       1985                300             20
        14          5       1985                300             40
        15          5       1965                300            240

相关问题：选择数字范围不重叠的地方

Answer 1

我的主要 DBMS 是 Teradata，但这也可以在 Oracle 中按原样工作。

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;

如果您需要返回实际覆盖的内容from/to_meas（如编辑前的问题），它可能会更复杂。第一部分是相同的，但没有聚合查询可以返回具有相同 event_id 的相邻行（例如，对于事件 3：0-1 和 1-25）：

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

如果要合并相邻行，则需要多两个步骤（使用标准方法，标记组的第一行并计算组号）：

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);

编辑：

Ups，我刚刚发现了一个博客Overlapping Ranges with priority与一些简化的 Oracle 语法完全相同。事实上，我将查询从 Teradata 中的其他一些简化语法翻译为标准/Oracle SQL :-)

Answer 2

还有另一种计算方法，使用 from 和 to 值：

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小提琴

Answer 3

今天想太多了，但是我现在有些东西忽略了+/- 10米。

首先制作了一个函数，它将对/从对作为字符串接收并返回字符串中对所覆盖的距离。例如 '10:20;35:45' 返回 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;

然后编写了这个查询，该查询为该函数在适当的先验范围内构建了一个字符串。无法对 list_agg 使用窗口化，但能够通过相关子查询实现相同的目的。

--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在这里：http ://sqlfiddle.com/#!4/81331/36

在我看来，结果与您的相符。我在最终查询中留下了额外的列以尝试说明每个步骤。

在测试用例上工作 - 可能需要一些工作来处理更大数据集中的所有可能性，但我认为这将是一个开始和完善的好地方。

重叠范围合并的信用是这里的第一个答案：合并重叠日期间隔

list_agg with windowing 的功劳是这里的第一个答案： LISTAGG 等价于 windowing 子句

Answer 4

我对您的“道路事件”有疑问，因为您没有描述什么是 1st meas，我认为它是 0 和 1 之间没有 1 的时期。

所以，你可以用一个查询来计算：

with newest_MEAS as (
select ROAD_ID, MEAS.m, max(year) y
from road_events
join (select rownum -1 m 
      from dual 
      connect by rownum -1 <= (select max(TOTAL_ROAD_LENGTH) from road_events) ) MEAS
  on MEAS.m between FROM_MEAS and TO_MEAS
group by ROAD_ID, MEAS.m )
select re.event_id, nm.ROAD_ID, re.total_road_length, nm.y, count(nm.m) EVENT_LENGTH
from newest_MEAS nm
join road_events re 
  on nm.ROAD_ID = re.ROAD_ID
  and nm.m between re.from_meas and re.to_meas -1
  and nm.y = re.year
group by re.event_id, nm.ROAD_ID, re.total_road_length, nm.y
order by event_id

SQL小提琴

Answer 5

解决方案：

SELECT RE.road_id, RE.event_id, RE.year, RE.from_meas, RE.to_meas, RE.road_length, RE.event_length, RE.used_length, RE.leftover_length
  FROM
  (
    SELECT RE.C_road_id[road_id], RE.C_event_id[event_id], RE.C_year[year], RE.C_from_meas[from_meas], RE.C_to_meas[to_meas], RE.C_road_length[road_length],
           RE.event_length, RE.used_length, (RE.event_length - (CASE WHEN RE.HasOverlap = 1 THEN RE.used_length ELSE 0 END))[leftover_length]
      FROM
      (
        SELECT RE.C_road_id, RE.C_event_id, RE.C_year, RE.C_from_meas, RE.C_to_meas, RE.C_road_length,
               (CASE WHEN MAX(RE.A_event_id) IS NOT NULL THEN 1 ELSE 0 END)[HasOverlap],
               (RE.C_to_meas - RE.C_from_meas)[event_length],
               SUM(   (CASE WHEN RE.O_to_meas <= RE.C_to_meas THEN RE.O_to_meas ELSE RE.C_to_meas END)
                    - (CASE WHEN RE.O_from_meas >= RE.C_from_meas THEN RE.O_from_meas ELSE RE.C_from_meas END)
                  )[used_length]--This is the length that is already being counted towards later years.
          FROM
          (
            SELECT RE.C_road_id, RE.C_event_id, RE.C_year, RE.C_from_meas, RE.C_to_meas, RE.C_road_length,
                   RE.A_event_id, MIN(RE.O_from_meas)[O_from_meas], MAX(RE.O_to_meas)[O_to_meas]
              FROM
              (
                SELECT RE_C.road_id[C_road_id], RE_C.event_id[C_event_id], RE_C.year[C_year], RE_C.from_meas[C_from_meas], RE_C.to_meas[C_to_meas], RE_C.total_road_length[C_road_length],
                       RE_A.road_id[A_road_id], RE_A.event_id[A_event_id], RE_A.year[A_year], RE_A.from_meas[A_from_meas], RE_A.to_meas[A_to_meas], RE_A.total_road_length[A_road_length],
                       RE_O.road_id[O_road_id], RE_O.event_id[O_event_id], RE_O.year[O_year], RE_O.from_meas[O_from_meas], RE_O.to_meas[O_to_meas], RE_O.total_road_length[O_road_length],
                       (ROW_NUMBER() OVER (PARTITION BY RE_C.road_id, RE_C.event_id, RE_O.event_id ORDER BY RE_S.Overlap DESC, RE_A.event_id))[RowNum]--Use to Group Overlaps into Swaths.
                  FROM road_events as RE_C--Current.
                  LEFT JOIN road_events as RE_A--After.  --Use a Left-Join to capture when there is only 1 Event (or it is the Last-Event in the list).
                    ON RE_A.road_id   = RE_C.road_id
                   AND RE_A.event_id != RE_C.event_id--Not the same EventID.
                   AND RE_A.year     >= RE_C.year--Occured on or After the Current Event.
                   AND (    (RE_A.from_meas >= RE_C.from_meas AND RE_A.from_meas <= RE_C.to_meas)--There is Overlap.
                         OR (RE_A.to_meas   >= RE_C.from_meas AND RE_A.to_meas   <= RE_C.to_meas)--There is Overlap.
                         OR (RE_A.to_meas    = RE_C.to_meas   AND RE_A.from_meas  = RE_C.from_meas)--They are Equal.
                       )
                  LEFT JOIN road_events as RE_O--Overlapped/Linked.
                    ON RE_O.road_id   = RE_C.road_id
                   AND RE_O.event_id != RE_C.event_id--Not the same EventID.
                   AND RE_O.year     >= RE_C.year--Occured on or After the Current Event.
                   AND (    (RE_O.from_meas >= RE_A.from_meas AND RE_O.from_meas <= RE_A.to_meas)--There is Overlap.
                         OR (RE_O.to_meas   >= RE_A.from_meas AND RE_O.to_meas   <= RE_A.to_meas)--There is Overlap.
                         OR (RE_O.to_meas    = RE_A.to_meas   AND RE_O.from_meas  = RE_A.from_meas)--They are Equal.
                       )
                  OUTER APPLY
                  (
                    SELECT COUNT(*)[Overlap]
                      FROM road_events as RE_O--Overlapped/Linked.
                     WHERE RE_O.road_id   = RE_C.road_id
                       AND RE_O.event_id != RE_C.event_id--Not the same EventID.
                       AND RE_O.year     >= RE_C.year--Occured on or After the Current Event.
                       AND (    (RE_O.from_meas >= RE_A.from_meas AND RE_O.from_meas <= RE_A.to_meas)--There is Overlap.
                             OR (RE_O.to_meas   >= RE_A.from_meas AND RE_O.to_meas   <= RE_A.to_meas)--There is Overlap.
                             OR (RE_O.to_meas    = RE_A.to_meas   AND RE_O.from_meas  = RE_A.from_meas)--They are Equal.
                           )
                  ) AS RE_S--Swath of Overlaps.
              ) AS RE
             WHERE RE.RowNum = 1--Remove Duplicates and Select those that are in the biggest Swaths.
             GROUP BY RE.C_road_id, RE.C_event_id, RE.C_year, RE.C_from_meas, RE.C_to_meas, RE.C_road_length,
                      RE.A_event_id
          ) AS RE
         GROUP BY RE.C_road_id, RE.C_event_id, RE.C_year, RE.C_from_meas, RE.C_to_meas, RE.C_road_length
      ) AS RE
  ) AS RE
 WHERE RE.leftover_length > 0--Filter out Events that had their entire Segments overlapped by a Later Event(s).
 ORDER BY RE.road_id, RE.year DESC, RE.event_id

SQL 小提琴：
    http ://sqlfiddle.com/#!18/2880b/1

添加的规则/假设/澄清：
1.) 考虑到可能性event_id，并且road_id可能是 Guid 的或乱序创建的，
    因此不要编写脚本假设更高或更低的值赋予记录关系以意义。
    例如：
      ID 为 1 和 ID 为 2 并不能保证 ID 为 2 是最新的（反之亦然）。
      这样解决方案将更加通用且不那么“hacky”。
2.) 过滤掉其整个段与后来的事件重叠的事件。
    例如：
      如果 2008 年在 20-50 有工作，而 2009 年在 10-60 有工作，
      那么 2008 年的事件将被过滤掉，因为它的整个段在 2009 年被重新散列。

附加测试数据：
为了确保解决方案不仅仅针对给定的 DataSet，
    我在原始 DataSet 中添加了road_id6个，以便解决更多的边缘情况。

INSERT INTO road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) VALUES (16,6,2012,0,100,100);
INSERT INTO road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) VALUES (17,6,2013,68,69,100);
INSERT INTO road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) VALUES (18,6,2014,65,66,100);
INSERT INTO road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) VALUES (19,6,2015,62,63,100);
INSERT INTO road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) VALUES (20,6,2016,50,60,100);
INSERT INTO road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) VALUES (21,6,2017,30,40,100);
INSERT INTO road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) VALUES (22,6,2017,20,55,100);
INSERT INTO road_events (event_id, road_id, year, from_meas, to_meas, total_road_length) VALUES (23,6,2018,0,25,100);

结果：（我在绿色中添加了8条附加记录）

数据库版本：
此解决方案与 Oracle 和 SQL-Server 无关：
    它应该适用于SS2008 + 和Oracle 12c +。

这个问题被标记为Oracle 12c，但是我没有注册就可以使用在线小提琴，
    所以我在 SQL-Server 中对其进行了测试——但相同的语法应该适用于两者。对于我的大部分查询，
我都依赖Cross-Apply和处理。 Oracle 在 12c 中引入了这些“联接”：https ://oracle-base.com/articles/12c/lateral-inline-views-cross-apply-and-outer-apply-joins-12cr1Outer-Apply

   

简化和高性能：
这使用：
    • 无相关子查询。
    • 无递归。
    • 没有CTE。
    • 没有工会。
    • 没有用户功能。

索引：
我读到了您就索引提出的问题之一。
我将为您将要搜索和分组的每个主要字段添加 1 列索引：
    road_id、event_id和year。
您可以查看此索引是否对您有任何帮助（我不知道您打算如何使用数据）：
    Key Fields: road_id , event_id, year
    Include: from_meas ,to_meas

标题：
您可能需要考虑将此问题的标题重命名为更易于搜索的名称，例如：
    “聚合重叠段以测量有效长度”。
这将使解决方案更容易找到，以帮助其他有类似问题的人。

其他想法：这样的事情在计算花费在     开始和停止时间戳重叠
的事情上的总时间时很有用。

Answer 6

这个发现扩展了表格，为每条道路的每英里生成一行，并且只需要MAX一年。然后我们可以COUNT根据行数来产生event_length。

它完全按照您上面指定的方式生成表格。

注意：我对 SQL Server 运行了这个查询。我认为您可以在 Oracle 中使用LEAST而不是。SELECT MIN(event_length) FROM (VALUES...)

WITH NumberRange(result) AS 
(
    SELECT 0
    UNION ALL
    SELECT result + 1
    FROM   NumberRange 
    WHERE  result < 301 --Max length of any road
),
CurrentRoadEventLength(road_id, [year], event_length) AS
(
    SELECT road_id, [year], COUNT(*) AS event_length
    FROM   (
            SELECT re.road_id, n.result, MAX(re.[year]) as [year]
            FROM   road_events re INNER JOIN NumberRange n 
                   ON (    re.from_meas <= n.result 
                       AND re.to_meas > n.result
                      )
            GROUP BY re.road_id, n.result
           ) events_per_mile
    GROUP BY road_id, [year]
)
SELECT re.event_id, re.road_id, re.[year], re.total_road_length, 
       (SELECT MIN(event_length) FROM (VALUES (re.to_meas - re.from_meas), (cre.event_length)) AS EventLengths(event_length))
FROM   road_events re INNER JOIN CurrentRoadEventLength cre
       ON (    re.road_id = cre.road_id
           AND re.[year] = cre.[year]
          )
ORDER BY re.event_id, re.road_id
OPTION (MAXRECURSION 301) --Max length of any road