Re: Full table scan

[Justin Cave]

At 09:08 PM 2/4/2003, you wrote:

I'm doing a select from 2 tables joining them using a primary key- ref
key on the tables and the explain plan is showing 2 full table scans...
Even after analyzing the tables and the Optimizer mode is set to CHOOSE.

SELECT a.col1, b.col2
  FROM table1 a, table2 b
 WHERE a.col1 = b.col1

Unless you have an index on (table2.col1, table2.col2), Oracle is going to have to go to table b for col2. Assuming that most rows in table2 will be involved in the results of the join, it's cheaper for Oracle to do a FTS on table2 than to do the join using only the PK indexes and then look up the value of col2 in the table.


Justin Cave
Distributed Database Consulting

--
Please see the official ORACLE-L FAQ: http://www.orafaq.net
--
Author: Justin Cave
INET: [EMAIL PROTECTED]

Fat City Network Services -- 858-538-5051 http://www.fatcity.com
San Diego, California -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from). You may
also send the HELP command for other information (like subscribing).