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Frequently Asked Questions (FAQ) for PostgreSQL
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- Last updated: Sun Jun 23 17:16:13 EDT 2002
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+ Last updated: Mon Jun 24 21:45:50 EDT 2002
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Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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using an index with ORDER BY and LIMIT:
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SELECT col
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FROM tab
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- ORDER BY col
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+ ORDER BY col [ DESC ]
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LIMIT 1
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When using wild-card operators such as LIKE or ~, indexes can only be
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- used if the beginning of the search is anchored to the start of the
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- string. Therefore, to use indexes, LIKE patterns must not start with
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- %, and ~(regular expression) patterns must start with ^.
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+ used if the default C local is used during initdb and the beginning of
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+ the search is anchored to the start of the string. Therefore, to use
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+ indexes, LIKE patterns must not start with %, and ~(regular
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+ expression) patterns must start with ^.
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4.9) How do I see how the query optimizer is evaluating my query?
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Original file line number Diff line number Diff line change 14
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alink ="#0000ff ">
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< H1 > Frequently Asked Questions (FAQ) for PostgreSQL</ H1 >
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- < P > Last updated: Sun Jun 23 17:16:13 EDT 2002</ P >
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+ < P > Last updated: Mon Jun 24 21:45:50 EDT 2002</ P >
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< P > Current maintainer: Bruce Momjian (< A href =
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"mailto:pgman@candle.pha.pa.us "> pgman@candle.pha.pa.us</ A > )< BR >
@@ -946,12 +946,13 @@ <H4><A name="4.8">4.8</A>) My queries are slow or don't make use of
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< PRE >
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SELECT col
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FROM tab
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- ORDER BY col
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+ ORDER BY col [ DESC ]
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LIMIT 1
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</ PRE >
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< P > When using wild-card operators such as < SMALL > LIKE</ SMALL > or
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- < I > ~</ I > , indexes can only be used if the beginning of the search
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+ < I > ~</ I > , indexes can only be used if the default C local is used
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+ during initdb and the beginning of the search
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is anchored to the start of the string. Therefore, to use indexes,
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< SMALL > LIKE</ SMALL > patterns must not start with < I > %</ I > , and
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< I > ~</ I > (regular expression) patterns must start with < I > ^</ I > .</ P >
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