MySQL 8.0

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CREATE TABLE test (
    id_1 INT,
    id_2 INT,
    ids VARCHAR(255) AS (CONCAT(LEAST(id_1, id_2), ' ', GREATEST(id_1, id_2))) STORED,
    PRIMARY KEY(ids),
    CHECK (id_1 <> id_2)
);
INSERT INTO test (id_1, id_2) VALUES (1,2), (1,3), (2,3);
INSERT INTO test (id_1, id_2) VALUES (2,1);
Duplicate entry '1 2' for key 'test.PRIMARY'

INSERT INTO test (id_1, id_2) VALUES (2,2);
Check constraint 'test_chk_1' is violated.