unique couples

unique_couples.sql

--Найти уникальные маршруты прямой-обратный и без обратных и отобразить только прямые
CREATE TABLE IF NOT EXISTS unique_couples
(
    point1 text,
    point2 text
);

INSERT INTO unique_couples VALUES('1','2');
INSERT INTO unique_couples VALUES('1','2');
INSERT INTO unique_couples VALUES('2','1');
INSERT INTO unique_couples VALUES('a','b');
INSERT INTO unique_couples VALUES('b','a');
INSERT INTO unique_couples VALUES('c','d');
INSERT INTO unique_couples VALUES('d','k');
INSERT INTO unique_couples VALUES('e','l');
INSERT INTO unique_couples VALUES('f','t');

SELECT * FROM (SELECT DISTINCT * FROM unique_couples
EXCEPT
SELECT DISTINCT t1.point2 AS u1,
    t2.point2 AS u2
   FROM unique_couples t1,
    unique_couples t2
  WHERE t1.point2 = t2.point1 AND t1.point1 < t2.point1) r ORDER BY point1;