MySQL 8.0

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CREATE TABLE s_product ( id INT, rating FLOAT)
SELECT 1 id, 1 rating UNION
SELECT 755, 1 UNION ALL
SELECT 755, NULL
UPDATE s_product
SET rating = FLOOR(40 + (RAND() * 11)) / 10
WHERE id = 755
SELECT * FROM s_product


id
rating


1
1

755
4.3

755
4.6