# \d user
                          Table "public.user"
  Column  |  Type   |                     Modifiers
----------+---------+---------------------------------------------------
 id       | integer | not null default nextval('user_id_seq'::regclass)
 username | text    |
 password | text    |
Indexes:
    "user_pkey" PRIMARY KEY, btree (id)
Referenced by:
    TABLE "vmail" CONSTRAINT "vmail_user_id_fkey" FOREIGN KEY (user_id) REFERENCES "user"(id)

=# \d vmail
                          Table "public.vmail"
 Column  |  Type   |                     Modifiers
---------+---------+----------------------------------------------------
 id      | integer | not null default nextval('vmail_id_seq'::regclass)
 user_id | integer |
 name    | text    |
Indexes:
    "vmail_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
    "vmail_user_id_fkey" FOREIGN KEY (user_id) REFERENCES "user"(id)