MySQL 8.0

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CREATE TABLE refs (id INTEGER PRIMARY KEY, custom_7 VARCHAR(10));
INSERT INTO refs (id) VALUES
(1), (2), (3), (4), (5), (6), (7), (8), (9), (10), 
(11), (12), (13), (14), (15), (16), (17), (18), (19), (20); 
UPDATE refs SET custom_7 = '';
WITH cte AS (SELECT *, ROW_NUMBER() OVER (ORDER BY id) rn FROM refs)
UPDATE refs r
INNER JOIN cte c ON c.id = r.id
SET r.custom_7 = (c.rn - 1) DIV 4 + 1;
SELECT * FROM refs;


id
custom_7


1
1

2
1

3
1

4
1

5
2

6
2

7
2

8
2

9
3

10
3

11
3

12
3

13
4

14
4

15
4

16
4

17
5

18
5

19
5

20
5