79 lines
4.6 KiB
HTML
79 lines
4.6 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 name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Grouping and joins with DB2 Multisystem" />
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<meta name="abstract" content="If the query contains a join, the partitioning key used to determine the type of grouping that can be implemented is based on any repartitioning of data that was required to implement the join." />
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<meta name="description" content="If the query contains a join, the partitioning key used to determine the type of grouping that can be implemented is based on any repartitioning of data that was required to implement the join." />
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<meta name="DC.subject" content="grouping, with joins, join, with grouping" />
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<meta name="keywords" content="grouping, with joins, join, with grouping" />
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<meta name="DC.Relation" scheme="URI" content="grouping.htm" />
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<meta name="DC.Relation" scheme="URI" content="grouping.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.Identifier" content="groupjoin" />
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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>Grouping and joins with DB2 Multisystem</title>
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</head>
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<body id="groupjoin"><a name="groupjoin"><!-- --></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">Grouping and joins with DB2<sup>®</sup> Multisystem</h1>
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<div><p>If the query contains a join, the partitioning key used to determine
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the type of grouping that can be implemented is based on any repartitioning
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of data that was required to implement the join.</p>
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<div class="section"><p>In the following example, a repartitioned join is performed before
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the grouping, which results in a new partitioning key of MGRNO. Because MGRNO
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is now the partitioning key, grouping can be performed using one-step grouping.
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</p>
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<p>SQL statement:</p>
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<pre> SELECT MGRNO, COUNT(*)
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FROM DEPARTMENT, EMPLOYEE
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WHERE MGRNO = EMPNO
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GROUP BY MGRNO
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</pre>
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<p>OPNQRYF command:</p>
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<pre> OPNQRYF FILE((DEPARTMENT) (EMPLOYEE)) FORMAT(GRPFMT2)
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JFLD((MGRNO EMPNO *EQ))
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GRPFLD(MGRNO)
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MAPFLD((CNTMGR '%COUNT'))</pre>
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<p>In the following
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example, a repartitioned join is performed before the grouping,
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which results in a new partitioning key of EMPNO. Because EMPNO is now the
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partitioning key instead of WORKDEPT, grouping cannot be performed using one-step
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grouping. </p>
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<p>SQL statement:</p>
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<pre> SELECT WORKDEPT, COUNT(*)
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FROM DEPARTMENT, EMPLOYEE
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WHERE MGRNO = EMPNO
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GROUP BY WORKDEPT
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</pre>
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<p>OPNQRYF command:</p>
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<pre> OPNQRYF FILE((DEPARTMENT) (EMPLOYEE)) FORMAT(GRPFMT3)
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JFLD((MGRNO EMPNO *EQ))
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GRPFLD(WORKDEPT)
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MAPFLD((CNTDEPT '%COUNT'))</pre>
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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="grouping.htm" title="The implementation method for grouping in queries that use distributed files is dependent on whether the partitioning key is included in the grouping criteria.">Implementation and optimization of grouping with DB2 Multisystem</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="grouping.htm" title="The implementation method for grouping in queries that use distributed files is dependent on whether the partitioning key is included in the grouping criteria.">Implementation and optimization of grouping with DB2 Multisystem</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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