Thread

1. 'now' runtime

   Karel Zak <zakkr@zf.jcu.cz> — 2005-04-07T11:13:04Z

   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>
   
   
   

2. Re: 'now' runtime

   Tom Lane <tgl@sss.pgh.pa.us> — 2005-04-07T14:14:27Z

   Karel Zak <zakkr@zf.jcu.cz> writes:
   > Why is there so different "Total runtime" for ('now'::text)::date) and
   > '2005-04-06'::date ?
   
   > I think both is constant during execution.
   
   Not at all. text_date() is not immutable so it has to be applied during
   execution.  The other one is just a constant.
   
   			regards, tom lane