Execution Plans and Casts

Does anybody know how the planner treats casts?
It seems as if casts are not taken into consideration when planning the 
query because the costs  seem to stay the same.


[hs@backup mag]$ psql -p 5400 test -c "EXPLAIN SELECT id FROM t_data1"                           QUERY PLAN
-------------------------------------------------------------------Seq Scan on t_data1  (cost=0.00..168966.00 rows=10000000 width=4)
(1 row)

[hs@backup mag]$ psql -p 5400 test -c "EXPLAIN SELECT id::numeric FROM 
t_data1"                           QUERY PLAN
-------------------------------------------------------------------Seq Scan on t_data1  (cost=0.00..168966.00 rows=10000000 width=4)
(1 row)

[hs@backup mag]$ psql -p 5400 test -c "EXPLAIN SELECT id::text FROM t_data1"                           QUERY PLAN
-------------------------------------------------------------------Seq Scan on t_data1  (cost=0.00..168966.00 rows=10000000 width=4)
(1 row)

[hs@backup mag]$ psql -p 5400 test -c "EXPLAIN SELECT COUNT(id::text) 
FROM t_data1"                              QUERY PLAN
-------------------------------------------------------------------------Aggregate  (cost=193966.00..193966.00 rows=1 width=4)  ->  Seq Scan on t_data1  (cost=0.00..168966.00 rows=10000000 width=4)
(2 rows)

[hs@backup mag]$ psql -p 5400 test -c "EXPLAIN SELECT COUNT(id) FROM 
t_data1"                              QUERY PLAN
-------------------------------------------------------------------------Aggregate  (cost=193966.00..193966.00 rows=1 width=4)  ->  Seq Scan on t_data1  (cost=0.00..168966.00 rows=10000000 width=4)
(2 rows)

   Hans