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Oracle SQL "like clause" and index access

Oracle Tips by Burleson Consulting

Indexing when using the SQL "like" clause can be tricky because the wildcard "%" operator can invalidate the index.  For example a last_name index would be OK with a "like 'SMI%'" query, but unusable with "like '%SMI%'.

Solutions to this issue of a leading wildcard can be addressed in several ways::

  • Context indexes - You can use Oracle text indexes to remove full-table scans when using the LIKE operator.
     
  • Index hint  - Laurent Schneider describes a procedure to replace the full-table scan with an index fast full scan using an index hint.
     
  • Case insensitive searching - The new 10g release 2 feature for case insensitive searches.

alter session set NLS_COMP=ANSI;
alter session set NLS_SORT=GENERIC_BASELETTER;
select * from customer where full_name = 'Don Burleson'

 

For more details, see my new book "Oracle Tuning: The Definitive Reference". 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


 

 

 

 
 
 
 
 

 
 
 
 
 
 
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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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