Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Mailing Lists -> Oracle-L -> Re: strange cost in explain plan

Re: strange cost in explain plan

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Sat, 13 Oct 2007 08:39:59 +0100
Message-ID: <013f01c80d6c$4293f140$0200a8c0@Primary>

Again, you are quoting a statement that isn't strictly true.

    "The access order is from top to bottom if the indent is the same"

First, it's only an approximation in simple execution plans anyway, and should be restated more like: "the order of operation of the child lines of a single parent is from top to bottom (assuming you've printed the plan correctly)".

But then the whole "scalar subquery in the select list" is a special case. I agree that visually it would make a little more sense to show the driving query first and then list the subqueries, but it's just not done that way.

I thought your example would be of sufficient general interest that I've written a little blog item about it. It doesn't say anything I haven't put in these email messages, though.

    http://jonathanlewis.wordpress.com/2007/10/12/scalar-subqueries/

Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com

Author: Cost Based Oracle: Fundamentals
http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html

--
http://www.freelists.org/webpage/oracle-l
Received on Sat Oct 13 2007 - 02:39:59 CDT

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US