SQL Server 2014

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CREATE TABLE your_table (
 ValidFrom DATE, 
 ValidTo DATE, 
 Num INT, 
 [ID Number] INT
)
INSERT INTO your_table 
  (ValidFrom,   	ValidTo, 	Num, 	[ID Number] ) 
VALUES
  ('2019-06-01', 	'2019-12-31', 	100, 	01234567) 
, ('2020-01-01', 	'2020-03-31', 	100, 	01234567) 
, ('2020-04-01', 	'2020-12-31', 	100, 	01234567) 
, ('2021-01-01', 	'2021-01-31', 	100, 	01234567) 
, ('2021-02-01', 	'2021-03-31', 	50, 	01234567) 
, ('2021-04-01', 	'2021-09-30', 	50, 	01234567) 
, ('2021-10-01', 	'2021-12-31', 	50, 	01234567) 
, ('2022-01-01', 	'2022-04-30', 	100, 	01234567) 
8 rows affected

-- rank via ascending row_number + descending row_number
SELECT
  MIN(ValidFrom) AS ValidFrom
, MAX(ValidTo) AS ValidTo
, Num
, [ID Number]
, Rnk
FROM
(
    SELECT *
    , Rnk = ROW_NUMBER() OVER (PARTITION BY [ID Number] ORDER BY ValidFrom ASC, ValidTo ASC)
          + ROW_NUMBER() OVER (PARTITION BY [ID Number], Num ORDER BY ValidFrom DESC, ValidTo DESC)
    FROM your_table
) q
GROUP BY [ID Number], Num, Rnk
ORDER BY [ID Number], MIN(ValidFrom)


ValidFrom
ValidTo
Num
ID Number
Rnk


2019-06-01
2021-01-31
100
1234567
6

2021-02-01
2021-12-31
50
1234567
8

2022-01-01
2022-04-30
100
1234567
9


-- rank via ascending row_number - ascending row_number
SELECT
  MIN(ValidFrom) AS ValidFrom
, MAX(ValidTo) AS ValidTo
, Num
, [ID Number]
, Rnk
FROM
(
    SELECT *
    , Rnk = ROW_NUMBER() OVER (PARTITION BY [ID Number] ORDER BY ValidFrom ASC, ValidTo ASC)
          - ROW_NUMBER() OVER (PARTITION BY [ID Number], Num ORDER BY ValidFrom ASC, ValidTo ASC)
    FROM your_table
) q
GROUP BY [ID Number], Num, Rnk
ORDER BY [ID Number], MIN(ValidFrom)


ValidFrom
ValidTo
Num
ID Number
Rnk


2019-06-01
2021-01-31
100
1234567
0

2021-02-01
2021-12-31
50
1234567
4

2022-01-01
2022-04-30
100
1234567
3


-- rank via summing flag on change
SELECT
  MIN(ValidFrom) AS ValidFrom
, MAX(ValidTo) AS ValidTo
, Num
, [ID Number]
, Rnk
FROM
(
  SELECT *
  , Rnk = SUM(flag) OVER (PARTITION BY [ID Number] ORDER BY ValidFrom, ValidTo)
  FROM
  (
    SELECT *
    , flag = IIF(Num = LAG(Num) OVER (PARTITION BY [ID Number] ORDER BY ValidFrom, ValidTo), 0, 1)
    FROM your_table
  ) q1
) q2
GROUP BY [ID Number], Num, Rnk
ORDER BY [ID Number], MIN(ValidFrom)


ValidFrom
ValidTo
Num
ID Number
Rnk


2019-06-01
2021-01-31
100
1234567
1

2021-02-01
2021-12-31
50
1234567
2

2022-01-01
2022-04-30
100
1234567
3
ValidFrom	ValidTo	Num	ID Number	Rnk
2019-06-01	2021-01-31	100	1234567	6
2021-02-01	2021-12-31	50	1234567	8
2022-01-01	2022-04-30	100	1234567	9