-<!-- $PostgreSQL: pgsql/doc/src/sgml/indices.sgml,v 1.58 2006/08/25 04:06:44 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/indices.sgml,v 1.59 2006/09/04 19:58:02 momjian Exp $ -->
<chapter id="indexes">
<title id="indexes-title">Indexes</title>
<quote>x < 1</quote> implies <quote>x < 2</quote>; otherwise
the predicate condition must exactly match part of the query's
<literal>WHERE</> condition
- or the index will not be recognized to be usable.
+ or the index will not be recognized to be usable. Matching takes
+ place at query planning time, not at run time. As a result,
+ parameterized query clauses will not work with a partial index. For
+ example a prepared query with a parameter might specify
+ <quote>x < ?</quote> which will never imply
+ <quote>x < 2</quote> for all possible values of the parameter.
</para>
<para>