MySQL 8.0

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CREATE TABLE op_country (id INT, op_id INT, country_id INT);
INSERT INTO op_country VALUES
(1  ,   1    ,    1),
(2  ,   1    ,    2),
(3  ,   2    ,    2),
(4  ,   2    ,    3),
(5  ,   3    ,    3),
(6  ,   3    ,    3),
(7  ,   1    ,    1);
SELECT * FROM op_country;


id
op_id
country_id


1
1
1

2
1
2

3
2
2

4
2
3

5
3
3

6
3
3

7
1
1


DELETE t1
FROM op_country t1
JOIN op_country t2 USING (op_id, country_id)
WHERE t1.id > t2.id
SELECT * FROM op_country;


id
op_id
country_id


1
1
1

2
1
2

3
2
2

4
2
3

5
3
3