SQL Server 2019

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CREATE TABLE mytable(
   Age    INT NOT NULL PRIMARY KEY
  ,Period INTEGER 
  ,Year   INTEGER 
);
INSERT INTO mytable(Age,Period,Year) VALUES ('0',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('1',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('2',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('3',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('4',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('5',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('6',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('7',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('8',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('9',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('10',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('11',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('12',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('13',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('14',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('15',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('16',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('17',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('18',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('19',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('20',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('21',46,2065);
INSERT INTO mytable(Age,Period,Year) VALUES ('22',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('23',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('24',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('25',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('26',51,2070);
INSERT INTO mytable(Age,Period,Year) VALUES ('27',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('28',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('29',NULL,NULL);
INSERT INTO mytable(Age,Period,Year) VALUES ('30',NULL,NULL);
31 rows affected


select t.age, 
    coalesce(t.period, n.period - n.diff, p.period - p.diff) period,
    coalesce(t.year, n.year     - n.diff, p.year   - p.diff) year
from mytable t
outer apply (
	select top (1) t1.*, t1.age - t.age diff
	from mytable t1 
	where t1.age > t.age and t1.period is not null and t1.year is not null
	order by t1.age 
) n
outer apply (
	select top (1) t1.*, t1.age - t.age diff
	from mytable t1 
	where t1.age < t.age and t1.period is not null and t1.year is not null
	order by t1.age desc
) p
order by t.age


age
period
year


0
25
2044

1
26
2045

2
27
2046

3
28
2047

4
29
2048

5
30
2049

6
31
2050

7
32
2051

8
33
2052

9
34
2053

10
35
2054

11
36
2055

12
37
2056

13
38
2057

14
39
2058

15
40
2059

16
41
2060

17
42
2061

18
43
2062

19
44
2063

20
45
2064

21
46
2065

22
47
2066

23
48
2067

24
49
2068

25
50
2069

26
51
2070

27
52
2071

28
53
2072

29
54
2073

30
55
2074


select
	age,
	coalesce(
	    period,
	    max(period) over(partition by grp2) - max(age) over(partition by grp2) + age,
	    max(period) over(partition by grp1) - min(age) over(partition by grp1) + age
	) period,
	coalesce(
	    year,
	    max(year) over(partition by grp2) - max(age) over(partition by grp2) + age,
	    max(year) over(partition by grp1) - min(age) over(partition by grp1) + age
	) year
from (
	select t.*, 
	    count(period) over(order by age) grp1, 
	    count(period) over(order by age desc) grp2
	from mytable t
) t
order by age


age
period
year


0
25
2044

1
26
2045

2
27
2046

3
28
2047

4
29
2048

5
30
2049

6
31
2050

7
32
2051

8
33
2052

9
34
2053

10
35
2054

11
36
2055

12
37
2056

13
38
2057

14
39
2058

15
40
2059

16
41
2060

17
42
2061

18
43
2062

19
44
2063

20
45
2064

21
46
2065

22
47
2066

23
48
2067

24
49
2068

25
50
2069

26
51
2070

27
52
2071

28
53
2072

29
54
2073

30
55
2074


Warning: Null value is eliminated by an aggregate or other SET operation.
age	period	year
0	25	2044
1	26	2045
2	27	2046
3	28	2047
4	29	2048
5	30	2049
6	31	2050
7	32	2051
8	33	2052
9	34	2053
10	35	2054
11	36	2055
12	37	2056
13	38	2057
14	39	2058
15	40	2059
16	41	2060
17	42	2061
18	43	2062
19	44	2063
20	45	2064
21	46	2065
22	47	2066
23	48	2067
24	49	2068
25	50	2069
26	51	2070
27	52	2071
28	53	2072
29	54	2073
30	55	2074