Re: Re: explain plan conundrum

The join order of an access plan - in the absence of any leading or ordered hints - is determined strictly like everything else by the CBO: the join order with the lowest estimated cost wins. And the selectivity and cardinality estimates play a big role in determining the cardinality and thus cost estimates.
To answer your question "does oracle use histograms and distinctness in determining join order?" outright: Yes, but only indirectly: histograms and distinctness determine the cardinality -> therefore the cost estimates -> therefore the join order.
And lastly, you can not compare the results, i.e. plans, of two different parses. Each is in its own world.

At 10:04 AM 11/5/2003, you wrote:
>im not concerned about the type of join. Im strictly concerned about the
>join order. does oracle use histograms and distinctness in determining
>join order? The odd thing is that it chose a different join order on these
>tables earlier and on 'similiar' joins(ie large number of records and only
>4 distinct values on the join column) oracle chooses the proper join 'order'
> >

Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com

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Author: Wolfgang Breitling
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