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1 | | -<!-- $PostgreSQL: pgsql/doc/src/sgml/indices.sgml,v 1.58 2006/08/25 04:06:44 tgl Exp $ --> |
| 1 | +<!-- $PostgreSQL: pgsql/doc/src/sgml/indices.sgml,v 1.59 2006/09/04 19:58:02 momjian Exp $ --> |
2 | 2 |
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3 | 3 | <chapter id="indexes"> |
4 | 4 | <title id="indexes-title">Indexes</title> |
@@ -679,7 +679,12 @@ SELECT * FROM orders WHERE order_nr = 3501; |
679 | 679 | <quote>x < 1</quote> implies <quote>x < 2</quote>; otherwise |
680 | 680 | the predicate condition must exactly match part of the query's |
681 | 681 | <literal>WHERE</> condition |
682 | | - or the index will not be recognized to be usable. |
| 682 | + or the index will not be recognized to be usable. Matching takes |
| 683 | + place at query planning time, not at run time. As a result, |
| 684 | + parameterized query clauses will not work with a partial index. For |
| 685 | + example a prepared query with a parameter might specify |
| 686 | + <quote>x < ?</quote> which will never imply |
| 687 | + <quote>x < 2</quote> for all possible values of the parameter. |
683 | 688 | </para> |
684 | 689 |
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685 | 690 | <para> |
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