Re: best practices with index on varchar column - Mailing list pgsql-performance

PFC <lists@boutiquenumerique.com> writes:
>> Can I use an index on a varchar column to optimize the SELECT queries
>> that use " column LIKE 'header%'  "?

>     Yes

>     Note that if you want case insensitive matching you need to make an index
> on lower(column) and SELECT WHERE lower(column) LIKE 'header%'

>     Locales may bite you.

Yes.  If your database locale is not "C" then the default btree index
behavior does not match up with what LIKE needs.  In that case you need
a special index using the appropriate "pattern_ops" opclass, eg

CREATE INDEX test_index ON test_table (col varchar_pattern_ops);

or if you want case insensitive matching

CREATE INDEX test_index ON test_table (lower(col) varchar_pattern_ops);

and then write the queries with lower() as PFC illustrates.  *Don't* use
ILIKE --- it basically can't use indexes at all.

For more info see
http://www.postgresql.org/docs/8.0/static/indexes-opclass.html

            regards, tom lane