SQL Server 2019

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CREATE TABLE #yourtable (grp int, Age int, Period int, Yr int)
INSERT INTO #yourtable (grp, Age, Period, Yr)
VALUES
(1, 0 ,  NULL,    NULL),
(1, 1 ,  NULL,    NULL),
(1, 2 ,  NULL,    NULL),
(1, 3 ,  NULL,    NULL),
(1, 4 ,  NULL,    NULL),
(1, 5 ,  NULL,    NULL),
(1, 6 ,  NULL,    NULL),
(1, 7 ,  NULL,    NULL),
(1, 8 ,  NULL,    NULL),
(1, 9 ,  NULL,    NULL),
(1, 10,  NULL,    NULL),
(1, 11,  NULL,    NULL),
(1, 12,  NULL,    NULL),
(1, 13,  NULL,    NULL),
(1, 14,  NULL,    NULL),
(1, 15,  NULL,    NULL),
(1, 16,  NULL,    NULL),
(1, 17,  NULL,    NULL),
(1, 18,  NULL,    NULL),
(1, 19,  NULL,    NULL),
(1, 20,  NULL,    NULL),
(1, 21,     2,    2021),
(1, 22,  NULL,    NULL),
(1, 23,  NULL,    NULL),
(1, 24,  NULL,    NULL),
(1, 25,  NULL,    NULL),
(1, 26,  null  ,  null),
(1, 27,  NULL,    NULL),
(1, 28,  NULL,    NULL),
(1, 29,  NULL,    NULL),
(1, 30,  NULL,    NULL);
31 rows affected

with cte as
 (
   select age
     ,max(period - age) over () + age as period
     ,max(yr - age) over() + age as yr
   from #yourtable
 )
select age
  ,case when period >0 then period end as period
  ,yr
from cte


age
period
yr


0
null
2000

1
null
2001

2
null
2002

3
null
2003

4
null
2004

5
null
2005

6
null
2006

7
null
2007

8
null
2008

9
null
2009

10
null
2010

11
null
2011

12
null
2012

13
null
2013

14
null
2014

15
null
2015

16
null
2016

17
null
2017

18
null
2018

19
null
2019

20
1
2020

21
2
2021

22
3
2022

23
4
2023

24
5
2024

25
6
2025

26
7
2026

27
8
2027

28
9
2028

29
10
2029

30
11
2030


Warning: Null value is eliminated by an aggregate or other SET operation.


; WITH	PeriodInc AS (SELECT TOP 1 Period - Age AS PeriodInc FROM #yourtable WHERE Period IS NOT NULL),
	YrInc AS (SELECT TOP 1 Yr - Age AS YrInc FROM #yourtable WHERE Yr IS NOT NULL)
SELECT	Age, 
	CASE WHEN (Age + PeriodInc) >= 0 THEN (Age + PeriodInc) ELSE NULL END AS Period, 
	Age + YrInc AS Yr
FROM	#yourtable
	CROSS JOIN PeriodInc
	CROSS JOIN YrInc


Age
Period
Yr


0
null
2000

1
null
2001

2
null
2002

3
null
2003

4
null
2004

5
null
2005

6
null
2006

7
null
2007

8
null
2008

9
null
2009

10
null
2010

11
null
2011

12
null
2012

13
null
2013

14
null
2014

15
null
2015

16
null
2016

17
null
2017

18
null
2018

19
0
2019

20
1
2020

21
2
2021

22
3
2022

23
4
2023

24
5
2024

25
6
2025

26
7
2026

27
8
2027

28
9
2028

29
10
2029

30
11
2030

age	period	yr
0	null	2000
1	null	2001
2	null	2002
3	null	2003
4	null	2004
5	null	2005
6	null	2006
7	null	2007
8	null	2008
9	null	2009
10	null	2010
11	null	2011
12	null	2012
13	null	2013
14	null	2014
15	null	2015
16	null	2016
17	null	2017
18	null	2018
19	null	2019
20	1	2020
21	2	2021
22	3	2022
23	4	2023
24	5	2024
25	6	2025
26	7	2026
27	8	2027
28	9	2028
29	10	2029
30	11	2030