Re: Full table scan

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

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