Hi, I'm using group by in both queries - group by gender The first query returns 4 tuples The second query returns 2 tuples I always thought that any filter that you apply should increase the speed Thanks, Dariusz. Niels Nes wrote:
On Wed, Jan 28, 2009 at 04:51:34PM +0100, Stefan Manegold wrote:
On Wed, Jan 28, 2009 at 09:54:35AM -0500, dariuszs wrote:
Hi, Could you please help me with this query? I've got gender field in the table1 with values 'Female', 'Male', 'Unknown' sql1: select gender,count(*) from table1 group by gender returns results in 2 seconds sql2: select gender,count(*) from table where gender in ('Female','Male') group by gender returns results in 20 seconds
Why the second query took longer when I'm selecting less values? Thanks.
a) Because your request grouging in the second case, but not in the first case, i.e., more complex query => more time. b) How many less tuples do you get in the second case, i.e., how many tuples are there in total, and how many of them have "unkown" gender?
run
trace select gender,count(*) from table1 group by gender; and also for the second query. Then you see were the time is spend.
Niels
Stefan
Dariusz.
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