GROUP BY Vs. Sub SELECT

Hi,

I'm just getting familiar with EXPLAIN ANALYZE output, so I'd like to get
some help to identify which one of the following queries would be better:

teste=# EXPLAIN ANALYZE SELECT aa.avaliacao_id, MAX(aa.avaliacao_versao) AS
avaliacao_versao, a.avaliacao_nome, aa.editar
teste-# FROM teo01tb104_areas_avaliacoes aa, teo01tb201_avaliacoes a
teste-# WHERE aa.avaliacao_id=10
teste-# AND aa.avaliacao_id=a.avaliacao_id
teste-# GROUP BY aa.avaliacao_id, a.avaliacao_nome, aa.editar;
                                                                    QUERY
PLAN
----------------------------------------------------------------------------
-----------------------------------------------------------------------
 HashAggregate  (cost=45.93..45.94 rows=1 width=52) (actual
time=0.466..0.469 rows=1 loops=1)
   ->  Nested Loop  (cost=4.04..45.66 rows=27 width=52) (actual
time=0.339..0.356 rows=1 loops=1)
         ->  Bitmap Heap Scan on teo01tb201_avaliacoes a  (cost=2.01..8.49
rows=3 width=47) (actual time=0.219..0.223 rows=1 loops=1)
               Recheck Cond: (avaliacao_id = 10)
               ->  Bitmap Index Scan on teo01tb201_avaliacoes_pk
(cost=0.00..2.01 rows=3 width=0) (actual time=0.166..0.166 rows=1 loops=1)
                     Index Cond: (avaliacao_id = 10)
         ->  Bitmap Heap Scan on teo01tb104_areas_avaliacoes aa
(cost=2.03..12.30 rows=9 width=9) (actual time=0.060..0.066 rows=1 loops=1)
               Recheck Cond: (avaliacao_id = 10)
               ->  Bitmap Index Scan on teo01tb104_areas_avaliacoes_pk
(cost=0.00..2.03 rows=9 width=0) (actual time=0.040..0.040 rows=1 loops=1)
                     Index Cond: (avaliacao_id = 10)
 Total runtime: 1.339 ms
(11 rows)

teste=# SELECT a.avaliacao_id, a.avaliacao_versao, a.avaliacao_nome,
aa.editar
teste-# FROM teo01tb201_avaliacoes a, teo01tb104_areas_avaliacoes aa
teste-# WHERE a.avaliacao_id=10
teste-# AND a.avaliacao_versao=(SELECT MAX(avaliacao_versao)
teste(#                         FROM teo01tb201_avaliacoes
teste(#                         WHERE avaliacao_id=10)
teste-# AND a.avaliacao_id=aa.avaliacao_id;
 avaliacao_id | avaliacao_versao | avaliacao_nome | editar
--------------+------------------+----------------+--------
           10 |                1 | Teste          | t
(1 row)

teste=# EXPLAIN ANALYZE SELECT a.avaliacao_id, a.avaliacao_versao,
a.avaliacao_nome, aa.editar
teste-# FROM teo01tb201_avaliacoes a, teo01tb104_areas_avaliacoes aa
teste-# WHERE a.avaliacao_id=10
teste-# AND a.avaliacao_versao=(SELECT MAX(avaliacao_versao)
teste(#                         FROM teo01tb201_avaliacoes
teste(#                         WHERE avaliacao_id=10)
teste-# AND a.avaliacao_id=aa.avaliacao_id;

QUERY PLAN
----------------------------------------------------------------------------
----------------------------------------------------------------------------
------------------------
 Nested Loop  (cost=6.20..22.38 rows=9 width=52) (actual time=0.573..0.596
rows=1 loops=1)
   InitPlan
     ->  Result  (cost=4.16..4.17 rows=1 width=0) (actual time=0.315..0.319
rows=1 loops=1)
           InitPlan
             ->  Limit  (cost=0.00..4.16 rows=1 width=4) (actual
time=0.257..0.261 rows=1 loops=1)
                   ->  Index Scan Backward using teo01tb201_avaliacoes_pk on
teo01tb201_avaliacoes  (cost=0.00..12.48 rows=3 width=4) (actual
time=0.245..0.245 rows=1 loops=1)
                         Index Cond: (avaliacao_id = 10)
                         Filter: (avaliacao_versao IS NOT NULL)
   ->  Index Scan using teo01tb201_avaliacoes_pk on teo01tb201_avaliacoes a
(cost=0.00..5.83 rows=1 width=51) (actual time=0.410..0.420 rows=1 loops=1)
         Index Cond: ((avaliacao_id = 10) AND (avaliacao_versao = $1))
   ->  Bitmap Heap Scan on teo01tb104_areas_avaliacoes aa  (cost=2.03..12.30
rows=9 width=5) (actual time=0.110..0.114 rows=1 loops=1)
         Recheck Cond: (avaliacao_id = 10)
         ->  Bitmap Index Scan on teo01tb104_areas_avaliacoes_pk
(cost=0.00..2.03 rows=9 width=0) (actual time=0.074..0.074 rows=1 loops=1)
               Index Cond: (avaliacao_id = 10)
 Total runtime: 1.418 ms
(15 rows)


I think 2nd would be better, since when database grow up the GROUP BY may
become too costly. Is that right?

Regards,
Bruno