SELECT u.* FROM edges u
WHERE currtag = 'person';

SELECT u.* FROM edges u, edges v, relations r
WHERE u.currtag = 'person'
  AND v.currtag = 'creditcard'
  AND u.currid = r.ancestor
  AND v.currid = r.descendant;

(SELECT u.* FROM edges u
WHERE currtag = 'person')
EXCEPT
(SELECT u.* FROM edges u, edges v, relations r
WHERE u.currtag = 'person'
  AND v.currtag = 'creditcard'
  AND u.currid = r.ancestor
  AND v.currid = r.descendant);