Merge Segment Ranges Based on Grouped Value - sql-server

Question

I have a table of segments with a beginning point, an ending point, and a value like so:
Bmp | Emp | SomeVal
0 1 1
1 2 1
2 3 2
3 4 2
4 5 1
I would like to merge (summarize) these records so they look like so:
Bmp | Emp | SomeVal
0 2 1
2 4 2
4 5 1
I've simplified my data set for the purpose of this question. The end result is I need unique rows grouped by the SomeVal column (in my real data set, there are about 20 columns) with the segments stitched together from Bmp to Emp, but not overlapping.
I've tried the following:
DECLARE #tbl TABLE (Bmp int, Emp int, SomeVal int)
INSERT INTO #tbl
SELECT 0, 1, 1 UNION
SELECT 1, 2, 1 UNION
SELECT 2, 3, 2 UNION
SELECT 3, 4, 2 UNION
SELECT 4, 5, 1
SELECT MIN(Bmp) AS Bmp, Max(Emp) AS Emp, SomeVal FROM #tbl
GROUP BY SomeVal
Unfortunately, it comes out like so which is wrong:
Bmp | Emp | SomeVal
0 5 1
2 4 2
My query above only works if the values of SomeVal do not repeat. How can I fix my sql?
Minimum required version is SQL 2008.

Answer 1

You may using ROW_NUMBER() function to correlate begin group row with end group row.
DECLARE #tbl TABLE (Bmp int, Emp int, SomeVal int)
INSERT INTO #tbl
SELECT 0, 1, 1 UNION
SELECT 1, 2, 1 UNION
SELECT 2, 3, 2 UNION
SELECT 3, 4, 2 UNION
SELECT 4, 5, 1
;WITH
[Begins] AS
(
SELECT Bmp, SomeVal, ROW_NUMBER() OVER (ORDER BY Bmp) AS OrderNumber
FROM #tbl AS [Begin]
WHERE NOT EXISTS (
SELECT 1
FROM #tbl AS [Prev]
WHERE [Prev].Emp = [Begin].Bmp AND [Prev].SomeVal = [Begin].SomeVal)
),
[Ends] AS
(
SELECT Emp, SomeVal, ROW_NUMBER() OVER (ORDER BY Emp) AS OrderNumber
FROM #tbl AS [End]
WHERE NOT EXISTS (
SELECT 1
FROM #tbl AS [Next]
WHERE [Next].Bmp = [End].Emp AND [Next].SomeVal = [End].SomeVal)
)
SELECT [Begins].Bmp, [Ends].Emp, [Begins].SomeVal
FROM [Begins]
INNER JOIN [Ends]
ON [Begins].OrderNumber = [Ends].OrderNumber;

Answer 2

Here is another option...
IF OBJECT_ID('tempdb..#TestData', 'U') IS NOT NULL
DROP TABLE #TestData;
CREATE TABLE #TestData (
Bmp INT NOT NULL PRIMARY KEY CLUSTERED,
Emp INT NOT NULL,
SomeVal INT NOT NULL
);
INSERT #TestData (Bmp, Emp, SomeVal)
SELECT 0, 1, 1 UNION ALL
SELECT 1, 2, 1 UNION ALL
SELECT 2, 3, 2 UNION ALL
SELECT 3, 4, 2 UNION ALL
SELECT 4, 5, 1;
--==============================================
WITH
cte_GroupStart AS (
SELECT
td.Bmp,
td.Emp,
td.SomeVal,
GroupStart = CASE WHEN td.SomeVal = LAG(td.SomeVal, 1) OVER (ORDER BY td.Bmp) THEN NULL ELSE ROW_NUMBER() OVER (ORDER BY td.Bmp) END
FROM
#TestData td
),
cte_FillGroup AS (
SELECT
gs.Bmp,
gs.Emp,
gs.SomeVal,
AggGroup = MAX(gs.GroupStart) OVER (ORDER BY gs.Bmp) -- ROWS UNBOUNDED PRECEDING is implied and should work as expected 2008
FROM
cte_GroupStart gs
)
SELECT
Bmp = MIN(fg.Bmp),
Emp = MAX(fg.Emp),
fg.SomeVal
FROM
cte_FillGroup fg
GROUP BY
fg.AggGroup,
fg.SomeVal
ORDER BY
fg.AggGroup;