Postgres 10

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE items ("group" VARCHAR, index INTEGER, "limit" INTEGER, value INTEGER) ;

INSERT INTO items ("group", index, "limit", value) VALUES 
  ('A', 1, 2, 1), ('A', 2, NULL, 3), 
  ('B', 1, 3, 2), ('B', 2, NULL, 2), ('B', 3, 1, 3), ('B', 4, 2, 5), 
  ('C', 1, 2, 3), ('C', 2, 2, 3), ('C', 3, NULL, 4), ('C', 4, 5, 5) ;
10 rows affected

SELECT * FROM items ;


group
index
limit
value


A
1
2
1

A
2
null
3

B
1
3
2

B
2
null
2

B
3
1
3

B
4
2
5

C
1
2
3

C
2
2
3

C
3
null
4

C
4
5
5


SELECT *,
       MIN(CASE WHEN value < "limit" THEN index ELSE NULL END) 
              OVER (PARTITION by "group" ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING) AS next
FROM items


group
index
limit
value
next


A
1
2
1
null

A
2
null
3
null

B
1
3
2
null

B
2
null
2
null

B
3
1
3
null

B
4
2
5
null

C
1
2
3
null

C
2
2
3
null

C
3
null
4
null

C
4
5
5
null

group	index	limit	value	next
A	1	2	1	null
A	2	null	3	null
B	1	3	2	null
B	2	null	2	null
B	3	1	3	null
B	4	2	5	null
C	1	2	3	null
C	2	2	3	null
C	3	null	4	null
C	4	5	5	null