[ADMIN] Index not used. WHY?

[Andrei Bintintan]

Hi,   I have the following table: CREATE TABLE public.rights ( id int4 DEFAULT nextval('"rights_id_seq"'::text) NOT NULL, id_user int4 NOT NULL, id_modull int4 NOT NULL, CONSTRAINT rights_pkey PRIMARY KEY (id) ) and I created the following indexes: CREATE INDEX right_id_modull_idx ON rights USING btree (id_modull); CREATE INDEX right_id_user_idx ON rights USING btree (id_user); Now the problem: EXPLAIN SELECT * FROM rights r WHERE r.id_modull =15 returnes: Seq Scan on rights r (cost=0.00..12.30 rows=42 width=12) Filter: (id_modull = 15) EXPLAIN SELECT * FROM rights r WHERE r.id_user =15 returnes: Index Scan using right_id_user_idx on rights r (cost=0.00..8.35 rows=11 width=12) Index Cond: (id_user = 15) Question: Why the right_id_modull_idx is NOT USED at the 1st query and the second query the right_id_user_idx index is used. I don't understand this. Thanx in advance. Andy.