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Message from discussion wildcard search and full tablescans
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hpuxrac  
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 More options Dec 7 2006, 8:52 am
Newsgroups: comp.databases.oracle.server
From: "hpuxrac" <johnbhur...@sbcglobal.net>
Date: 7 Dec 2006 05:52:53 -0800
Local: Thurs, Dec 7 2006 8:52 am
Subject: Re: wildcard search and full tablescans
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wagen...@yahoo.com wrote:
> Oracle10g 10.2.0.1

> select * from <table_name> where <column_name> like '%abc%';

> does not use the index and does a full tablescan (guess this is the
> expected behaviour as per explain plan).

> Any suggestions as to how to use the index (index hint didn't help), IF
> possible or other alternatives.

> thanks

If you CANNOT begin the search with some leading characters ( not the
percent sign ) ... ie where some_col like 'abc%' ... then normally I
would expect to the optimizer to pick either a full table scan or some
kind of index scan.

You might want to do a 10053 trace and some analysis of where the
optimizer is going with your query.

You can put in a hint like this select /*+ INDEX(table_or_view_name
optional_index_name) */ column_list FROM etc ...

Eiher a full table scan or a full index scan ( of some type ) produces
an application that has scalability limitations built into it.  ( Your
logical IO's are very high ).

For full searching within a column there are options including the TEXT
indexes but they have some complications ( different SQL where syntax,
maintenance and cpu implications etc ).

Oracle will work nicely with regular character indexes IF you put a
where clause and a like that DOESN'T start with a percent sign.


 
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