70 lines
4.8 KiB
HTML
70 lines
4.8 KiB
HTML
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<?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 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="reference" />
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<meta name="DC.Title" content="Radix index" />
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<meta name="abstract" content="An SQL index (or keyed sequence access path) is a permanent object that is created over a table and used by the optimizer to provide a sequenced view of the data for a scan or probe operation." />
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<meta name="description" content="An SQL index (or keyed sequence access path) is a permanent object that is created over a table and used by the optimizer to provide a sequenced view of the data for a scan or probe operation." />
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<meta name="DC.subject" content="definitions, radix index, index, access method, radix index, radix index" />
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<meta name="keywords" content="definitions, radix index, index, access method, radix index, radix index" />
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<meta name="DC.Relation" scheme="URI" content="rzajqpermobj.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqrindscan.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzajqrinprobe.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="perf21b" />
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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>Radix index</title>
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</head>
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<body id="perf21b"><a name="perf21b"><!-- --></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">Radix index</h1>
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<div><p>An SQL index (or keyed sequence access path) is a permanent object
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that is created over a table and used by the optimizer to provide a sequenced
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view of the data for a scan or probe operation.</p>
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<div class="section"><p>The rows in the tables are sequenced in the index based upon the
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key columns specified on the creation of the object. When the key columns
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are matched up by the optimizer to a query, it gives the optimizer the ability
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to use the radix index to help satisfy any selection, ordering, grouping or
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join requirements.</p>
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</div>
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<div class="section"><p>Typically the use of an index operation will also include a Table
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Probe operation to provide access to any columns needed to satisfy the query
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that cannot be found as index keys. If all of the columns necessary to satisfy
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the query request for a table can be found as keys of an index, then the Table
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Probe is not required and the query uses Index Only Access. Avoiding the Table
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Probe can be an important savings for a query. The I/O associated with a Table
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Probe is typically the more expensive synchronous random I/O.</p>
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</div>
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<div class="section"><p>Visual Explain icon:</p>
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</div>
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<div class="section"><p><img src="rzajq506.gif" alt="Radix index icon" /></p>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rzajqrindscan.htm">Radix index scan</a></strong><br />
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A radix index scan operation is used to retrieve the rows from a table in a keyed sequence. Like a Table Scan, all of the rows in the index will be sequentially processed, but the resulting row numbers will be sequenced based upon the key columns.</li>
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<li class="ulchildlink"><strong><a href="rzajqrinprobe.htm">Radix index probe</a></strong><br />
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A radix index probe operation is used to retrieve the rows from a table in a keyed sequence. The main difference between the Radix Index Probe and the Radix Index Scan is that the rows being returned must first be identified by a probe operation to subset the rows being retrieved.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzajqpermobj.htm" title="The database objects and access methods used by the query engine can be broken down into three basic types of operations that are used to manipulate the permanent and temporary objects -- Create, Scan, and Probe.">Permanent objects and access methods</a></div>
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</div>
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</div>
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</body>
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</html>
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