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Don Burleson Blog

Oracle SQL "like clause" and index access

Oracle Database Tips by Donald Burleson

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 by 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'

See here, how to create a con*text Oracle text index.

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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