Driving Table in the execution plan

From: <sweidanz_at_yahoo.com>
Date: Tue, 4 Sep 2001 11:35:03 +1000
Message-ID: <0XWk7.1020$Qq2.1330@nsw.nnrp.telstra.net>

Hi All,
I was reading one of Oracle books and was surprised to find out that in Oracle the order of the table names in the FROM clause can make a difference in the execution plan.
Basically, the following as quoted:

"The execution plan chosen by Oracle determines a driving table based on
the order of the table names in the FROM clause. Rule-based: Oracle optimiser chooses the last table as the driving table. Cost-based : Oracle optimiser chooses the first table as the driving table"

Question1: Is that true in Oracle8i or it was on previous versions?

And as recommended by the Author:
"for the cost-based method order the tables with the smallest table first"

Question2: I don't really understand this recommendation. Why the smallest table should be the driving table?

Thanks,
ZS Received on Mon Sep 03 2001 - 20:35:03 CDT