MySQL 8.0

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select version();


version()


8.0.36


CREATE TABLE Client_Product ( 
Client VARCHAR(20) ,
Product VARCHAR(20) );

INSERT INTO  Client_Product  VALUES
('Alex','A'),
('Alex','B'),
('Alex','C'),
('Alex','D'),
('Peter','A'),
('Peter','B'),
('Peter','C'),
('Aline','C'),
('Aline','D'),
('Aline','E'),
('Aline','F'),
('Aline','G'),
('Joao','B'),
('Joao','C'),
('Joao','D'),
('Joao','E'),
('Nikky','A'),
('Nikky','B'),
('Nikky','C');


Records: 19  Duplicates: 0  Warnings: 0


SELECT CONCAT_WS(',', cp1.Product, cp2.Product, cp3.Product) AS ProductCombo, COUNT(*) AS Cnt
FROM Client_Product cp1
JOIN Client_Product cp2 ON cp1.Client = cp2.Client AND cp1.Product < cp2.Product
JOIN Client_Product cp3 ON cp2.Client = cp3.Client AND cp2.Product < cp3.Product
GROUP BY ProductCombo
ORDER BY Cnt DESC
LIMIT 1;


ProductCombo
Cnt


A,B,C
3