CREATE SEQUENCE test_seq;
CREATE TABLE test (
	id integer
		DEFAULT nextval('test_seq')
		CHECK(id > 0)
		PRIMARY KEY,
	parent integer
		CHECK((id = 1 AND parent IS NULL) OR (id <> 1 AND parent IS NOT NULL))
		REFERENCES test(id) ON DELETE CASCADE,
	data text
		NOT NULL
) WITHOUT OIDS;
INSERT INTO test VALUES(DEFAULT, NULL, 'root');	-- every tree has to have a root! (c) Joe Celko
CREATE TRIGGER test_insert BEFORE INSERT ON test FOR EACH ROW EXECUTE PROCEDURE tree_insert();
CREATE TRIGGER test_delete BEFORE DELETE ON test FOR EACH ROW EXECUTE PROCEDURE tree_delete();

CREATE TABLE test_tree (
	id integer NOT NULL REFERENCES test(id) ON DELETE CASCADE,
	node integer[2] NOT NULL,
	kids integer NOT NULL CHECK(kids >= 0),
	CONSTRAINT id_unique UNIQUE(id)
) WITHOUT OIDS;
INSERT INTO test_tree VALUES(1, ARRAY[3,2], 0);