Basically, that's correct. Oracle _generally_ does a good job choosing an
excellent execution path. In some cases better than can be achieved through
the Rule-based optimizer...However there's that 0.5% that we have to
manually tune. Check out the section on HINTS in your Oracle Docs...you have
a surprising amount of control.
Kevin Toepke
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-----Original Message-----
Sent: Friday, April 06, 2001 2:06 PM
To: Multiple recipients of list ORACLE-L
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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