Re: Question on how cardinality is calculated.

5% of num_rows

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

• Original Message ----- From: "Ronnie Doggart" <ronnie_doggart_at_lagan.com> To: <oracle-l_at_freelists.org> Sent: Thursday, January 10, 2008 3:06 PM Subject: Question on how cardinality is calculated.

All

Does anyone know how Oracle calculates the cardinality of a query such as:

Select * from table_1 where upper(case) like '%12345%';

Execution Plan

   0 SELECT STATEMENT Optimizer=CHOOSE (Cost=131 Card=5553 Bytes=621936)    1 0 TABLE ACCESS (FULL) OF 'TABLE_1' (Cost=131 Card=5553 Bytes=621936)

Oracle calculates that it is expecting 5553 rows from this query but I know it will only return 2.

How does it do its estimate ?

Ronnie Doggart

--

http://www.freelists.org/webpage/oracle-l Received on Thu Jan 10 2008 - 10:22:20 CST