Postgres 13

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CREATE TABLE if not EXISTS scores (
  id int,
  class char,
  score float
);

INSERT INTO scores VALUES
(1, 'A', 0.5),
(1, 'B', 0.2),
(1, 'C', 0.1),
(2, 'A', 0.1),
(2, 'B', 0.2),
(3, 'D', 0.01),
(4, 'A', 0.5),
(4, 'B', 0.5);
8 rows affected

SELECT DISTINCT ON (id) id, class
FROM scores 
ORDER BY id, random();


id
class


1
C

2
A

3
D

4
B


SELECT id, class 
FROM (
SELECT *, row_number() OVER (PARTITION BY id ORDER BY random()) as rn
FROM scores ) sub
WHERE rn = 1;


id
class


1
A

2
A

3
D

4
B