Cost based optimizer

I just got back from OOW and was reading a paper titled "Tuning Oracle SQL" (paper #171).

It talked about adding "hints" to SQL statements that were using the Cost based optimizer.

I thought the whole reason for using a cost based optimizer vs rules based was that the optimizer was suppose to be smart and determine the best path to get to the data (and thus making the coder of the SQL not have to know the physical DB design - so that when changes are made to the physical structure, you don't have to go out and change code "hints" or special ordering in the where clause).

So if you add hints to SQL statements that use cost based optimization (and collect statistics), what is the advantage of cost based over rules based optimizer ????????????

Thanks to anyone who can give me insight on this subject.

Art Received on Thu Nov 14 1996 - 00:00:00 CET