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CREATE TABLE tablename (
`A` VARCHAR(1),
`B` VARCHAR(1),
`C` VARCHAR(1)
);
INSERT INTO tablename
(`A`, `B`, `C`)
VALUES
('a', 'b', 'c'),
('a', 'b', 'd'),
('a', 'c', 'd'),
('b', 'a', 'c'),
('b', 'd', 'a');
SELECT A,
CONCAT('[', GROUP_CONCAT(DISTINCT B SEPARATOR ', '), ']') B,
CONCAT('[', GROUP_CONCAT(DISTINCT C SEPARATOR ', '), ']') C
FROM tablename
GROUP BY A
| A | B | C |
|---|---|---|
| a | [b, c] | [c, d] |
| b | [a, d] | [a, c] |