PostgreSQL Autoincrement

Yes, SERIAL is the equivalent function.

CREATE TABLE foo (
id SERIAL,
bar varchar);

INSERT INTO foo (bar) values ('blah');
INSERT INTO foo (bar) values ('blah');

SELECT * FROM foo;

1,blah
2,blah

SERIAL is just a create table time macro around sequences. You can not alter SERIAL onto an existing column.

You can use any other integer data type, such as smallint.

Example :

CREATE SEQUENCE user_id_seq;
CREATE TABLE user (
    user_id smallint NOT NULL DEFAULT nextval('user_id_seq')
);
ALTER SEQUENCE user_id_seq OWNED BY user.user_id;

Better to use your own data type, rather than user serial data type.

If you want to add sequence to id in the table which already exist you can use:

CREATE SEQUENCE user_id_seq;
ALTER TABLE user ALTER user_id SET DEFAULT NEXTVAL('user_id_seq');