56 lines
3.4 KiB
HTML
56 lines
3.4 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta name="Robots" content="index,follow" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Indexes" />
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<meta name="abstract" content="An SQL index is a subset of the data in the columns of a table that are logically arranged in either ascending or descending order." />
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<meta name="description" content="An SQL index is a subset of the data in the columns of a table that are logically arranged in either ascending or descending order." />
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<meta name="DC.subject" content="index, definition" />
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<meta name="keywords" content="index, definition" />
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<meta name="DC.Relation" scheme="URI" content="rbafysqlobjects.htm" />
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<meta name="DC.Relation" scheme="URI" content="../rzajq/efindex.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rbafyindexex" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Indexes</title>
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</head>
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<body id="rbafyindexex"><a name="rbafyindexex"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Indexes</h1>
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<div><p>An SQL <dfn class="term">index</dfn> is a subset of the data
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in the columns of a table that are logically arranged in either ascending
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or descending order.</p>
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<p>Each index contains a separate arrangement. These arrangements are used
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for ordering (ORDER BY clause), grouping (GROUP BY clause), and joining. An
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SQL index is a keyed logical file.</p>
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<p>The index is used by the system for faster data retrieval. Creating an
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index is optional. You can create any number of indexes. You can create or
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drop an index at any time. The index is automatically maintained by the system.
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However, because the indexes are maintained by the system, a large number
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of indexes can adversely affect the performance of applications that change
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the table.</p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafysqlobjects.htm" title="SQL objects are schemas, journals, catalogs, tables, aliases, views, indexes, constraints, triggers, sequences, stored procedures, user-defined functions, user-defined types, and SQL packages. SQL creates and maintains these objects as system objects.">SQL objects</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../rzajq/efindex.htm">Create an index strategy</a></div>
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</div>
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</div>
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</body>
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</html> |