T-SQL Combine Ranges Based On Value - sql

Question

I am using SQL Server 2012 and have been struggling with this query for hours. I am trying to aggregate mile post ranges based off the value in the Value column. The results should have unique segments with the highest value from the Value field for each segment. Here's an example:
Mile_Marker_Start | Mile_Marker_End | Value
0 100 5
50 150 6
100 200 10
75 300 9
150 200 7
And here's the result I'm looking for:
Mile_Marker_Start | Mile_Marker_End | Value
0 50 5
50 75 6
75 100 9
100 200 10
200 300 9
As you can see, the row with a value of 9 got split into 2 rows because Value 10 was bigger. Also, the row with Value 7 does not display because Value 10 was bigger. Can this be done without using a cursor? Any help would be much appreciated.
Thanks

Answer 1

I believe the following now does what you need. I'd recommend running all the parts separately so you can see what they do and how they work.
DECLARE #input AS TABLE
(Mile_Marker_Start int, Mile_Marker_End int, Value int)
INSERT INTO #input VALUES
(0,100,5), (50,150,6), (100,200,10), (75,300,9), (150,200,7)
DECLARE #staging as table
(Mile_Marker int)
INSERT INTO #staging
SELECT Mile_Marker_Start from #input
UNION -- this will remove duplicates
SELECT Mile_Marker_End from #input
; -- we need semi-colon for the following CTE
-- this CTE gets the right values, but the rows aren't "collapsed"
WITH all_markers AS
(
SELECT
groups.Mile_Marker_Start,
groups.Mile_Marker_End,
max(i3.Value) Value
FROM
(
SELECT
s1.Mile_Marker Mile_Marker_Start,
min(s2.Mile_Marker) Mile_Marker_End
FROM
#staging s1
JOIN #staging s2 ON
s1.Mile_Marker < s2.Mile_Marker
GROUP BY
s1.Mile_Marker
) as groups
JOIN #input i3 ON
i3.Mile_Marker_Start < groups.Mile_Marker_End AND
i3.Mile_Marker_End > groups.Mile_Marker_Start
GROUP BY
groups.Mile_Marker_Start,
groups.Mile_Marker_End
)
SELECT
MIN(collapse.Mile_Marker_Start) as Mile_Marker_Start,
MAX(collapse.Mile_Marker_End) as Mile_Marker_End,
collapse.Value
FROM
(-- Subquery get's IDs for the groups we're collapsing together
SELECT
am.*,
ROW_NUMBER() OVER (ORDER BY am.Mile_Marker_Start) - ROW_NUMBER() OVER (PARTITION BY am.Value ORDER BY am.Mile_Marker_Start) GroupID
FROM
all_markers am
) AS COLLAPSE
GROUP BY
collapse.GroupID,
collapse.Value
ORDER BY
MIN(collapse.Mile_Marker_Start)

Answer 2

Since you are on 2012 you could maybe use LEAD. Here is my code but as noted on your question by #stevelovell , we need clarification on how you are getting your result table.
--test date
declare #tablename TABLE
(
Mile_Marker_Start int,
Mile_Marker_End int,
Value int
);
insert into #tablename
values(0,100, 5),
(50,150, 6),
(100,200,10),
(75,300, 9),
(150,200, 7);
--query
select *
from #tablename
order by Mile_Marker_Start
select Mile_Marker_Start,
case when lead(mile_marker_start) over(order by mile_marker_start) < Mile_Marker_End THEN
lead(mile_marker_start) over(order by mile_marker_start)
ELSE
Mile_marker_end
END
AS MILE_MARKER_END,
Value
from #tablename
order by Mile_Marker_Start
Once you update your notes I will come back and update my answer.
Update: wasn't able to get LEAD and the other windowing functions to work with your requirements. With the way you need to move up and down the table current, and calculated values...