140 lines
8.3 KiB
HTML
140 lines
8.3 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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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Collocated join with DB2 Multisystem" />
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<meta name="abstract" content="In a collocated join, corresponding records of files being joined exist on the same node." />
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<meta name="description" content="In a collocated join, corresponding records of files being joined exist on the same node." />
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<meta name="DC.subject" content="query, collocated join, join, collocated, example, collocated join query" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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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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<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>Collocated join with DB2 Multisystem</title>
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</head>
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<body id="collocated"><a name="collocated"><!-- --></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">Collocated join with DB2<sup>®</sup> Multisystem</h1>
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<div><p>In a collocated join, corresponding records of files being joined
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exist on the same node.</p>
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<div class="section"><p>The values of the partitioning key of the files being joined are
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partition compatible. No data needs to be moved to another node to perform
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the join. This method is only valid for queries where all of the fields of
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the partitioning keys are join fields and the join operator is the = (equals)
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operator. Also, the nth field (where n=1 to the number of fields in the partitioning
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key) of the partitioning key of the first file must be joined to the nth field
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of the partitioning key of the second file, and the data types of the nth
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fields must be partition compatible. Note that all of the fields of the partitioning
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key must be involved in the join. Additional join predicates that do not contain
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fields of the partitioning key do not affect your ability to do a collocated
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join.</p>
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<p>In the following example, because the join predicate involves
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the partitioning key fields of both files and the fields are partition compatible,
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a collocated join can be performed. This implies that matching values of DEPTNO
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and WORKDEPT are located on the same node.</p>
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<p>SQL statement:</p>
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<pre> SELECT DEPTNAME, FIRSTNME, LASTNAME
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FROM DEPARTMENT, EMPLOYEE
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WHERE DEPTNO=WORKDEPT</pre>
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<p>OPNQRYF command:</p>
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<pre> OPNQRYF FILE((DEPARTMENT) (EMPLOYEE))
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FORMAT(JOINFMT)
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JFLD((DEPTNO WORKDEPT *EQ))</pre>
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<p>Records returned
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by this query:</p>
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<table cellpadding="4" cellspacing="0" border="1" class="tableborder"><tr><td>
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<table cellpadding="4" cellspacing="0" summary="" border="0"><caption>Table 1. Display of the query results</caption><thead align="left"><tr><th align="left" valign="bottom" width="33.33333333333333%" id="d0e75">DEPTNAME</th>
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<th align="left" valign="bottom" width="33.33333333333333%" id="d0e77">FIRSTNME</th>
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<th align="left" valign="bottom" width="33.33333333333333%" id="d0e79">LASTNAME</th>
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</tr>
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</thead>
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<tbody><tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e75 ">Support services</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e77 ">Christine</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e79 ">Haas</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e75 ">Support services</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e77 ">Sally</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e79 ">Kwan</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e75 ">Planning</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e77 ">John</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e79 ">Geyer</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e75 ">Planning</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e77 ">Irving</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e79 ">Stern</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e75 ">Accounting</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e77 ">Michael</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e79 ">Thompson</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e75 ">Accounting</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e77 ">Eileen</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e79 ">Henderson</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e75 ">Programming</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e77 ">Jennifer</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e79 ">Lutz</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e75 ">Programming</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e77 ">David</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e79 ">White</td>
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</tr>
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</tbody>
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</table>
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</td></tr></table>
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<div class="p">In the following example, the additional join predicate MGRNO=EMPNO
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does not affect the ability to perform a collocated join, because the partitioning
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keys are still involved in a join predicate. <pre>SQL: SELECT DEPTNAME, FIRSTNME, LASTNAME
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FROM DEPARTMENT, EMPLOYEE
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WHERE DEPTNO=WORKDEPT AND MGRNO=EMPNO</pre>
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<pre>OPNQRYF: OPNQRYF FILE((DEPARTMENT) (EMPLOYEE))
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FORMAT(JOINFMT)
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JFLD((DEPTNO WORKDEPT *EQ) (MGRNO EMPNO *EQ))</pre>
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</div>
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<p>Records
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returned by this query:</p>
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<table cellpadding="4" cellspacing="0" border="1" class="tableborder"><tr><td>
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<table cellpadding="4" cellspacing="0" summary="" border="0"><caption>Table 2. Display of the query
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results</caption><thead align="left"><tr><th align="left" valign="bottom" width="33.33333333333333%" id="d0e155">DEPTNAME</th>
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<th align="left" valign="bottom" width="33.33333333333333%" id="d0e157">FIRSTNME</th>
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<th align="left" valign="bottom" width="33.33333333333333%" id="d0e159">LASTNAME</th>
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</tr>
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</thead>
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<tbody><tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">Support services</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Christine</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 ">Haas</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e155 ">Accounting</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e157 ">Michael</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e159 ">Thompson</td>
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</tr>
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</tbody>
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</table>
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</td></tr></table>
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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="joins.htm" title="In addition to the performance considerations for nondistributed join queries, more performance considerations exist for queries involving distributed files.">Implementation and optimization of join operations 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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