Problem with a view (not lazy ;) - Mailing list pgsql-general

Hi all.

 In my tests with views I have found a problem that can't explain.

 Look at this view:
--------------------------------------
create view v_ingresos_técnico as
    select e.nombre as empleado, p.importe_total, p.iva, p.num_factura,
        p.fecha_factura, p.cobrado, a.urgente, ta.fecha
    from técnico_aviso ta
        join empleado e on ta.empleado = e.cod
        join presupuesto p on ta.aviso = p.aviso
        join aviso a on ta.aviso = a.número;
--------------------------------------

 When I query:

     SELECT empleado, sum(importe_total) from v_ingresos_técnico
    where fecha between '1/1/2002' and '31/1/2002' group by
    empleado;

 It executes inmediately. Here is the explain:
--------------------------------------
Aggregate  (cost=2930.48..2930.48 rows=1 width=40)
  ->  Group  (cost=2930.48..2930.48 rows=1 width=40)
        ->  Sort  (cost=2930.48..2930.48 rows=1 width=40)
              ->  Nested Loop  (cost=3.71..2930.47 rows=1 width=40)
                    ->  Nested Loop  (cost=3.71..2506.35 rows=177 width=36)
                          ->  Hash Join  (cost=3.71..1449.89 rows=510 width=24)
                                ->  Seq Scan on técnico_aviso ta  (cost=0.00..1424.06 rows=510 width=8)
                                ->  Hash  (cost=3.37..3.37 rows=137 width=16)
                                      ->  Seq Scan on empleado e  (cost=0.00..3.37 rows=137 width=16)
                          ->  Index Scan using pre_aviso_ndx on presupuesto p  (cost=0.00..2.06 rows=1 width=12)
                    ->  Index Scan using aviso_pkey on aviso a  (cost=0.00..2.39 rows=1 width=4)
--------------------------------------


 Now look at this view. Differences with previous are marked with "->":
--------------------------------------
create view v_ingresos_técnico as
    select e.nombre as empleado, p.importe_total, p.iva, p.num_factura,
        p.fecha_factura, p.cobrado, a.urgente, ta.fecha,
->        em.descripcion as empresa
    from técnico_aviso ta
        join empleado e on ta.empleado = e.cod
        join presupuesto p on ta.aviso = p.aviso
        join aviso a
->            left join empresa em on a.empresa = em.cod
            on ta.aviso = a.número;
--------------------------------------

 Executing same query it lags for more than a minute. Here is explain:
--------------------------------------
Aggregate  (cost=5679.37..5679.38 rows=1 width=46)
  ->  Group  (cost=5679.37..5679.37 rows=1 width=46)
        ->  Sort  (cost=5679.37..5679.37 rows=1 width=46)
              ->  Nested Loop  (cost=1.34..5679.36 rows=1 width=46)
                    ->  Nested Loop  (cost=0.00..6.28 rows=1 width=36)
                          ->  Nested Loop  (cost=0.00..4.21 rows=1 width=24)
                                ->  Index Scan using tec_avi_fecha_ndx on técnico_aviso ta  (cost=0.00..2.18 rows=1
width=8)
                                ->  Index Scan using empleado_pkey on empleado e  (cost=0.00..2.01 rows=1 width=16)
                          ->  Index Scan using pre_aviso_ndx on presupuesto p  (cost=0.00..2.06 rows=1 width=12)
                    ->  Materialize  (cost=4974.88..4974.88 rows=46547 width=10)
                          ->  Merge Join  (cost=1.34..4974.88 rows=46547 width=10)
                                ->  Index Scan using avi_empresa_ndx on aviso a  (cost=0.00..4391.56 rows=46547
width=6)
                                ->  Sort  (cost=1.34..1.34 rows=12 width=4)
                                      ->  Seq Scan on empresa em  (cost=0.00..1.12 rows=12 width=4)
---------------------------------------

 I am curious about "Materialize" but don't know what it means.

 Table "empresa" has 12 rows and there are indexes for all fields that
 participate in a join.

 Please, any help with this problem?.

 Thanks in advance.

                                 David