1
CREATE TABLE freundschaften (
person1 INT,
person2 INT,
PRIMARY KEY(person1, person2)
);2
Triggerfunktion
CREATE FUNCTION reverse_friendship() RETURNS TRIGGER AS
$$ BEGIN
INSERT INTO freundschaften VALUES (
NEW.person2, NEW.person1
) ON CONFLICT DO NOTHING;
RETURN NULL;
END $$ LANGUAGE plpgsql;Trigger
CREATE TRIGGER reverse_friendship
AFTER INSERT
ON freundschaften
FOR EACH ROW
EXECUTE PROCEDURE reverse_friendship();