index scan

Hello, pgsql-sql.

I have customize simple query with join two tables:

xxxx=# \d sites Таблица "public.sites" Колонка | Тип | Модификаторы
---------+------------------------+-----------------------
name | character varying(255) | not null
rem | text |
enabled | boolean | not null default true
Index:
"pk_sites" primary key, btree (oid)

xxxx=# \d site_screens
-------------+------------------------+--------------
id_site | oid | not null
screen_name | character varying(255) | not null
screen_code | text |
Foreign keys:
"$1" FOREIGN KEY (id_site) REFERENCES sites(oid)

xxxx=# explain select * from sites s join site_screens ss on s.oid = ss.id_site; QUERY PLAN ---------------------------------------------------------------------------
Hash Join (cost=...)
Hash Cond: ("outer".id_site = "inner".oid)
-> Seq Scan on site_screens ss (cost=...)
-> Hash (cost=...)
-> Seq Scan on sites s (cost=...)

I want to Index Scan. What must I do?

--
Regards,
Mihail Nasedkin
mailto:m(dot)nasedkin(dot)perm(at)mail(dot)ru