ALTER TABLE computer ALTER COLUMN compid SET DEFAULT nextval('computer_compid_seq'::regclass);

ALTER TABLE customers ALTER COLUMN uniqid SET DEFAULT nextval('customers_uniqid_seq'::regclass);

ALTER TABLE ONLY computer
    ADD CONSTRAINT computer_pkey PRIMARY KEY (compid);

ALTER TABLE ONLY customers
    ADD CONSTRAINT customers_pkey PRIMARY KEY (uniqid);

ALTER TABLE ONLY customerstocomputers
    ADD CONSTRAINT customerstocomputers_pkey PRIMARY KEY (custid, compid);

ALTER TABLE ONLY customerstocomputers
    ADD CONSTRAINT customerstocomputers_custid_fkey FOREIGN KEY (custid) REFERENCES customers(uniqid);

ALTER TABLE ONLY customerstocomputers
    ADD CONSTRAINT customerstocomputers_compid_fkey FOREIGN KEY (compid) REFERENCES computer(compid);