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Add section on testing index scan.

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Bruce Momjian 2003-01-17 17:15:14 +00:00
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Frequently Asked Questions (FAQ) for PostgreSQL Frequently Asked Questions (FAQ) for PostgreSQL
Last updated: Sun Jan 12 13:36:11 EST 2003 Last updated: Fri Jan 17 12:15:04 EST 2003
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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ORDER BY col [ DESC ] ORDER BY col [ DESC ]
LIMIT 1; LIMIT 1;
If you believe the optimizer is incorrect in choosing a sequential
scan, use SET enable_seqscan TO 'off' and run tests to see if an index
scan is indeed faster.
When using wild-card operators such as LIKE or ~, indexes can only be When using wild-card operators such as LIKE or ~, indexes can only be
used in certain circumstances: used in certain circumstances:
* The beginning of the search string must be anchored to the start * The beginning of the search string must be anchored to the start