RE: Index Behaviour

From: Mercadante, Thomas F <NDATFM_at_labor.state.ny.us>
Date: Fri, 06 Jul 2001 11:38:40 -0700
Message-ID: <F001.00343600.20010706115152@fatcity.com>

Dave,

I think <> is like using the NOT operator, thus an index can not be used.

Think about it - your asking the optimizer to find records in the index that are not there - nothing to really search on - so it does a FTS.

Now if you did

select surnam from basic where membno between 0 and 9

                         or    membno between 10 and 10000

it might work as expected.

hope this helps

Tom Mercadante
Oracle Certified Professional

-----Original Message-----
Sent: Friday, July 06, 2001 12:53 PM
To: Multiple recipients of list ORACLE-L

Hi,

In the following query "membno" is a Non Unique Indexed field:

select surnam from basic where membno <> 10.

Whether the table is analyzed or not the Explain Plan still shows a Full Table Scan unless I specify a Hint to use the Index. Using the index is more costly so I would expect CBO to always do a FTS unless the hint is specified. But without a hint why does RBO do a FTS and ignore the index?

Platform NT
Version 8.1.7.0.0
Optimizer Mode is Choose:

Many thanks for any replies

Dave Leach

PS. Like the Bear stories, being brought up in London we miss out on all this.

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Author: Dave Leach
INET: Dave.Leach_at_claybrook.co.uk

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Author: Mercadante, Thomas F
INET: NDATFM_at_labor.state.ny.us

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