58 lines
3.5 KiB
HTML
58 lines
3.5 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="Optimizing grouping by adding additional grouping columns" />
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<meta name="abstract" content="The same logic that is applied to removing grouping columns can also be used to add additional grouping columns to the query. This is only done when you are trying to determine if an index can be used to implement the grouping." />
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<meta name="description" content="The same logic that is applied to removing grouping columns can also be used to add additional grouping columns to the query. This is only done when you are trying to determine if an index can be used to implement the grouping." />
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<meta name="DC.Relation" scheme="URI" content="groupopt.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="rzajqgroupaddcols" />
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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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<!-- 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>Optimizing grouping by adding additional grouping columns</title>
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</head>
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<body id="rzajqgroupaddcols"><a name="rzajqgroupaddcols"><!-- --></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">Optimizing grouping by adding additional grouping columns</h1>
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<div><p>The same logic that is applied to removing grouping columns can
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also be used to add additional grouping columns to the query. This is only
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done when you are trying to determine if an index can be used to implement
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the grouping.</p>
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<div class="section"><p>The following example illustrates a query where the optimizer
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might add an additional grouping column. </p>
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<pre> <strong>CREATE INDEX</strong> X1 <strong>ON</strong> EMPLOYEE
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(LASTNAME, EMPNO, WORKDEPT)
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<strong>DECLARE</strong> DEPTEMP <strong>CURSOR FOR
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SELECT</strong> LASTNAME, WORKDEPT
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<strong>FROM</strong> CORPDATA.EMPLOYEE
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<strong>WHERE</strong> EMPNO = '000190'
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<strong>GROUP BY</strong> LASTNAME, WORKDEPT
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</pre>
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</div>
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<div class="section"><p>For this query request, the optimizer can add EMPNO as an additional
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grouping column when considering <samp class="codeph">X1</samp> for the query.</p>
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</div>
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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="groupopt.htm" title="DB2 Universal Database for iSeries has certain techniques to use when the optimizer encounters grouping. The query optimizer chooses its methods for optimizing your query.">Grouping optimization</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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