LaTeX-examples/documents/musterloesung-db-2012-09-24/d2c2.sql

SELECT f1.person2, f2.person2 
FROM (
    SELECT person2 FROM FriendshipSymmetric WHERE person1 = <id>
) f1
JOIN ON
(
    SELECT person2 FROM FriendshipSymmetric WHERE person1 = <id>
) f2
EXCEPT
(
    SELECT * FROM FriendshipSymmetric
)
WHERE f1.person2 != f2.person2