MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

select version();


version()


8.0.27


CREATE TABLE client(id INTEGER, name VARCHAR(200));

INSERT INTO client VALUES
   (1,'client 1'),
   (2,'client 2');
CREATE TABLE category(id INTEGER, name VARCHAR(200));

INSERT INTO category VALUES
   (1,'category 1'),
   (2,'catgory 2'),
   (3,'category 3');
CREATE TABLE client_category(id INTEGER, id_client INTEGER, id_category INTEGER);

INSERT INTO client_category VALUES
   (1,1,1),
   (2,2,1),
   (3,2,2),
   (3,2,3);
SELECT
   c.name, y.name
FROM client c
CROSS JOIN category y
LEFT JOIN client_category cc ON cc.id_client = c.id AND cc.id_category = y.id
WHERE cc.id IS NULL
ORDER BY c.id, y.id


name
name


client 1
catgory 2

client 1
category 3