Administración de PostgreSQL
EXPLAIN - tercer ejemplo de nuevo

alvh=# CREATE INDEX blah ON multi (primarioid);
CREATE
alvh=# EXPLAIN SELECT primario.primarioid FROM multi NATURAL JOIN primario ORDER BY primario.primarioid LIMIT 20;
NOTICE:  QUERY PLAN:

Limit  (cost=0.00..3.55 rows=20 width=8)
  ->  Merge Join  (cost=0.00..2663.06 rows=15000
                   width=8)
        ->  Index Scan using blah on multi
              (cost=0.00..644.00 rows=15000 width=4)
        ->  Index Scan using primario_pkey on primario
              (cost=0.00..1543.85 rows=100085 width=4)

EXPLAIN