Note in-line.
--
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
April 2004 Iceland http://www.index.is/oracleday.php
June 2004 UK - Optimising Oracle Seminar
"Paul" <pkelley_at_coat.com> wrote in message
news:473377b4.0403300744.4d535155_at_posting.google.com...
> From metalink:
>
> "Please note that the decision to unnest a subquery is not costed in
> Oracle9i. The decision to unnest a subquery is taken based on a set of
> heuristics (rules) before the query is optimized."
Just as a little extra on that, the 10g Performance Guide and Ref has
this to say about the UNNEST hint:
The UNNEST hint tells Oracle to check the subquery block for validity only.
If the
subquery block is valid, then subquery unnesting is enabled without checking
the
heuristics or costs.
The 9.2 manual does not have the words "or costs" at the end. This tends
to suggest that 10g (unhinted) does take costs into account when considering
unnesting. However, until I can find an example where 9i and 10g produce
different 10053 traces, I'm not going to commit myself on that just yet.
Received on Wed Mar 31 2004 - 01:58:21 CST
