SQL Server 2019

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SET NOCOUNT ON;

DROP TABLE IF EXISTS #tmpIncoming;

CREATE TABLE #tmpIncoming
(
  [Segment] int NOT NULL,
  [Weight]  int NOT NULL
);

INSERT INTO #tmpIncoming VALUES
( 1,  25),
( 2,  45),
( 3,  20),
( 4,  30),
( 5,  50),
( 6,  21),
( 7, 110);

DECLARE @nMaxChunkSize int = 100;
    
    ;WITH x AS 
    (
      SELECT Segment, 
             Weight, 
             rn = ROW_NUMBER() OVER (ORDER BY Segment)
        FROM #tmpIncoming
    ),
    cte AS 
    (
      SELECT Segment, Weight, rn, Total = Weight
      FROM x 
      WHERE rn = 1
      
      UNION ALL
    
      SELECT x.Segment, x.Weight, x.rn, Total = CASE 
        WHEN x.Weight + cte.Total > @nMaxChunkSize 
        THEN x.Weight ELSE x.Weight + cte.Total END
      FROM x JOIN cte ON x.rn = cte.rn + 1
    )
    SELECT MinSegment = MIN(Segment), 
           MaxSegment = MAX(Segment),
           Weight     = MAX(Total)
    FROM 
    (
      SELECT Segment, Total, 
        NewGroup = SUM(CASE WHEN Weight = Total THEN 1 ELSE 0 END) 
        OVER (ORDER BY Segment ROWS UNBOUNDED PRECEDING) FROM cte
    ) AS y
    GROUP BY NewGroup
    ORDER BY MinSegment;

-- BEGIN: suboptimal
DROP TABLE IF EXISTS #tmpResult;

CREATE TABLE #tmpResult
(
    [MinSegment] int NOT NULL,
    [MaxSegment] int NOT NULL,
    [Weight]   int NOT NULL
);

DECLARE cur CURSOR LOCAL READ_ONLY FORWARD_ONLY STATIC FOR
SELECT
    [Segment],
    [Weight]
FROM
    #tmpIncoming
ORDER BY
    [Segment];

OPEN cur;

DECLARE @nMinSegment int = 0, @nMaxSegment int = 0;
DECLARE @nWeightSoFar int = 0;

WHILE (1=1)
BEGIN
    DECLARE @nSegment int, @nWeight int;
    FETCH NEXT FROM cur INTO @nSegment, @nWeight;

IF (@@FETCH_STATUS <> 0)
        BREAK;

IF (@nWeightSoFar + @nWeight > @nMaxChunkSize)
    BEGIN
        INSERT INTO #tmpResult ([MinSegment], [MaxSegment], [Weight])
        VALUES (@nMinSegment, @nMaxSegment, @nWeightSoFar);

SET @nMinSegment = @nSegment;
        SET @nMaxSegment = @nSegment;
        SET @nWeightSoFar = @nWeight;
    END
    ELSE
    BEGIN
        IF (@nMinSegment = 0)
            SET @nMinSegment = @nSegment;
        SET @nMaxSegment = @nSegment;
        SET @nWeightSoFar = @nWeightSoFar + @nWeight;
    END;
END;

CLOSE cur;
DEALLOCATE cur;

IF (@nWeightSoFar > 0)
    INSERT INTO #tmpResult ([MinSegment], [MaxSegment], [Weight])
    VALUES (@nMinSegment, @nMaxSegment, @nWeightSoFar);

SELECT * FROM #tmpResult;

DROP TABLE IF EXISTS #tmpResult;
-- END: suboptimal

DROP TABLE IF EXISTS #tmp;

MinSegment	MaxSegment	Weight
1	3	90
4	5	80
6	6	21
7	7	110

MinSegment	MaxSegment	Weight
1	3	90
4	5	80
6	6	21
7	7	110