Re: Where clause order - importance of - rule based optimisation

In article <01bc43c3$5a377980$b1f876a5_at_Topas8>, Peter McKenzie <pemmck_at_ibm.net> writes
>My experience teaches me that this order is very important ,is bottom up,
>and that the from clause order is meaningless in the presence of a where
>clause which cites at least one indexed column. Many people disagree with
>me and various writers on performance give conflicting advice. Am I
>correct in my assumptions ? Does this rule change from one version of
>Oracle to another. Why is there still so much confusion with regard to
>tuning in the Oracle arena ?
>
You are more or less correct. Under the rule based optimiser, if an access path could not be worked out by applying the 17 rules to the where clause, then it used the order of tables in the from clause to determine the driving table. THe order of tables is a last resort tuning method, but it can be extremely effective.

The rules used to be documented in the dba guide, but they may have dropped that from recent versions.

-- 
Jim Smith