MySQL 8.0

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CREATE TABLE test (id INT, wishlist INT)
INSERT INTO test VALUES (4,13),(5,NULL),(6,NULL),(7,NULL),(21,14),(22,NULL),(23,NULL),(24,NULL)
SELECT * FROM test


id
wishlist


4
13

5
null

6
null

7
null

21
14

22
null

23
null

24
null


UPDATE test
SET wishlist = (@tmp:=COALESCE(wishlist, @tmp))
WHERE (@tmp:=-1)
ORDER BY id ASC
SELECT * FROM test


id
wishlist


4
13

5
13

6
13

7
13

21
14

22
14

23
14

24
14

id	wishlist
4	13
5	null
6	null
7	null
21	14
22	null
23	null
24	null