RE: Driving table

From: <A.SAXENA_at_ponl.com>
Date: Fri, 06 Apr 2001 10:27:28 -0700
Message-ID: <F001.002E4431.20010406100618@fatcity.com>

Hi there ,
Thanks for the reply .

I am in Cost Based Optimizer ( we all will be now a days ) .

Does that mean , if I want to know ( or decide ) while writting the query , my driving table , Its not possible ???
If I have a good idea ( size of data in tables , indexes etc.) about the tables involved in the join and I want to know before writting the query my driving table , I do not think I am expecting too much .

Please do reply .

Cheers .

Anup

First question is whether you're in Cost Based or Rule Based optimization. In RBO you are correct that it will read tables right to left unless instructed otherwise by a hint.

In CBO, Oracle will choose what it thinks is 'best', which most of the time, but not all of the time :), will be true.

Jay Miller

-----Original Message-----

Sent: Friday, April 06, 2001 6:45 AM
To: Multiple recipients of list ORACLE-L

Hi friends ,

I have got some query regarding , how the query is exactly executed ??

We always take joins and if we see the plan of the query , there is always one
main driving table . Some times I get feeling that , in the join the right most table is the driving table . But that is not always true , this is my observation from several plans .

In Oracle documentation alos ita mentioned that ( Server Concepts, 815 or 816
: Optimisation of Joins ), "one driving table is selected" , but at least I cannot makeout which of the several tables will be selected as driving table

What can be the potential criterions of selecting a driving table ?

Please , if you all can throw some light on the same or can redirect to some document , that would be great .

Cheers ,
Anup Saxena

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Author: Miller, Jay
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