Re: Question on how cardinality is calculated.
Date: Thu, 10 Jan 2008 16:22:20 -0000
5% of num_rows
Author: Cost Based Oracle: Fundamentals
The Co-operative Oracle Users' FAQ
- 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.
Does anyone know how Oracle calculates the cardinality of a query such as:
Select * from table_1 where upper(case) like '%12345%';
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 ?
http://www.freelists.org/webpage/oracle-l Received on Thu Jan 10 2008 - 10:22:20 CST