gistfile1.txt

postgres=# select * from identity_always;
 id | name
----+------
  1 | RJ
(1 row)

postgres=# alter table identity_always alter COLUMN id restart ;
ALTER TABLE


postgres=# insert into identity_always (name) values ('test');
ERROR:  duplicate key value violates unique constraint "identity_always_pkey"
DETAIL:  Key (id)=(1) already exists.

postgres=# truncate identity_always restart identity;
TRUNCATE TABLE

postgres=# insert into identity_always (name) values ('test');
INSERT 0 1
postgres=# select * from identity_always;
 id | name
----+------
  1 | test
(1 row)