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Help:select against partitions

From: Mike F <u518615722_at_spawnkill.ip-mobilphone.net>
Date: Wed, 20 Feb 2002 21:45:54 GMT
Message-ID: <l.1014241554.1937103271@[64.94.198.252]>


One of our big tables has 12 partitions on polltime, which is (Jan_2002,Feb_2002,Mar_2002,...Dec_2002). The table is fully analyzed.

When we use

Select ....
From Big_table
where polltime >
to_date('01/10/2002 11:00:00','MM/DD/YYYY HH24:MI:SS') AND polltime < to_date('01/10/2002 11:59:00','MM/DD/YYYY HH24:MI:SS')

the cost is about 9000.

but if we use

Select ....
From Big_table partition (Jan_2002)
where polltime >
to_date('01/10/2002 11:00:00','MM/DD/YYYY HH24:MI:SS') AND polltime < to_date('01/10/2002 11:59:00','MM/DD/YYYY HH24:MI:SS')

The cost is only 200.

Why oracle does not know which partition to go, and needs us to tell  him which partition?

Is there any way we can avoid of specifying WHICH partition in the query and still get the same performance?

Thanks for your help  

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