'now' runtime

Why is there so different "Total runtime" for ('now'::text)::date) and
'2005-04-06'::date ?

I think both is constant during execution.


 CREATE TABLE test (
      _time timestamp with time zone,
      _platform character(5),
      _tld character(5)
) WITHOUT OIDS;


explain analyze SELECT count(*) from test where
_time::date=CURRENT_DATE;
                                             QUERY PLAN
----------------------------------------------------------------------------------------------------
 Aggregate  (cost=0.01..0.01 rows=1 width=0) (actual time=0.026..0.029
rows=1 loops=1)
   ->  Seq Scan on test  (cost=0.00..0.00 rows=1 width=0) (actual
time=0.004..0.004 rows=0 loops=1)
         Filter: ((_time)::date = ('now'::text)::date)
 Total runtime: 24.034 ms
                ^^^^^^^^


explain analyze SELECT count(*) from test where
_time::date='2005-04-06'::date;
                                             QUERY PLAN
----------------------------------------------------------------------------------------------------
 Aggregate  (cost=0.01..0.01 rows=1 width=0) (actual time=0.015..0.018
rows=1 loops=1)
   ->  Seq Scan on test  (cost=0.00..0.00 rows=1 width=0) (actual
time=0.004..0.004 rows=0 loops=1)
         Filter: ((_time)::date = '2005-04-06'::date)
 Total runtime: 0.065 ms
                ^^^^^^^^

	Karel

-- 
Karel Zak <zakkr@zf.jcu.cz>