CREATE TABLE a(id int PRIMARY KEY, b_id int);
CREATE TABLE b(id int PRIMARY KEY);
ALTER TABLE a ADD CONSTRAINT a_b_id_fkey FOREIGN KEY(b_id) REFERENCES b(id);
INSERT INTO b VALUES (1), (2), (3);
INSERT INTO a VALUES (1, 1), (2, 2), (3, 2);
ALTER TABLE b ADD COLUMN id_tmp UUID NOT NULL DEFAULT uuid_generate_v1mc();
ALTER TABLE a ADD COLUMN b_id_tmp UUID;
UPDATE a SET b_id_tmp = b.id_tmp FROM b WHERE b.id = a.b_id;
ALTER TABLE a DROP COLUMN b_id;
ALTER TABLE a RENAME COLUMN b_id_tmp TO b_id;
ALTER TABLE b DROP COLUMN id;
ALTER TABLE b RENAME COLUMN id_tmp TO id;
ALTER TABLE b ADD PRIMARY KEY (id);
ALTER TABLE a ADD CONSTRAINT b_id_fkey FOREIGN KEY(b_id) REFERENCES b(id);