friends.sql

CREATE TABLE friends (
  person1 INT NOT NULL,
  person2 INT NOT NULL,
  PRIMARY KEY (person1, person2)
);

SELECT p.*
FROM people AS p
  INNER JOIN (
    SELECT person1 AS friend
    FROM friends
    WHERE (person2 = ?)
    UNION ALL
    SELECT person2 AS friend
    FROM friends
    WHERE (person1 = ?)
  ) AS f ON (p.personID = f.friend);