CREATE TABLE countries
(
  id serial NOT NULL,
  country_code varchar(5) NOT NULL,
  country varchar NOT NULL,
  "language" varchar(3),
  CONSTRAINT countries_pkey PRIMARY KEY (id)
) 

INSERT INTO "countries" ("country_code", "country", "language") VALUES ('AFG', 'Afghanistan', 'lt')
ERROR:  duplicate key violates unique constraint "countries_pkey"

However, if I manually set "id" it works. Any clues??