132 lines
7.6 KiB
HTML
132 lines
7.6 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="Directed join with DB2 Multisystem" />
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<meta name="abstract" content="In the directed join, the partitioning keys of at least one of the files are used as the join fields." />
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<meta name="description" content="In the directed join, the partitioning keys of at least one of the files are used as the join fields." />
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<meta name="DC.subject" content="query, directed join, join, directed, example, directed join query" />
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<meta name="keywords" content="query, directed join, join, directed, example, directed join query" />
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<meta name="DC.Relation" scheme="URI" content="joins.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="directed" />
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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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<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>Directed join with DB2 Multisystem</title>
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</head>
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<body id="directed"><a name="directed"><!-- --></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">Directed join with DB2<sup>®</sup> Multisystem</h1>
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<div><p>In the directed join, the partitioning keys of at least one of
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the files are used as the join fields.</p>
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<div class="section"><p>The join fields do not match the partitioning
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keys of the other files. Records of one file are directed to or sent to the
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nodes of the second file based on the hashing of the join field values using
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the partition map and node group of the second file. As soon as the records
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have been moved to the nodes of the second file through a temporary distributed
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file, a collocated join is used to join the data. This method is valid only
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for equijoin queries where all fields of the partitioning key are join fields
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for at least one of the files.</p>
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<p>In the following query, join field (WORKDEPT)
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is the partitioning key for file EMPLOYEE; however, join field (ADMRDEPT)
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is not the partitioning key for DEPARTMENT. If the join was attempted without
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moving the data, result records would be missing because record 2 of DEPARTMENT
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should be joined to records 1 and 2 of EMPLOYEE and these records are stored
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on different nodes. </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 ADMRDEPT = WORKDEPT AND JOB = 'Manager'</pre>
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<p>OPNQRYF
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command:</p>
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<pre> OPNQRYF FILE((DEPARTMENT) (EMPLOYEE))
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FORMAT(JOINFMT)
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QRYSLT('JOB *EQ 'Manager')
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JFLD((ADMRDEPT WORKDEPT *EQ))</pre>
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<p>The
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records of DEPARTMENT that are needed to run the query are read, and the data
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in ADMRDEPT is hashed using the partitioning map and the node group of EMPLOYEE.
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A temporary file is created and looks like this:</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. A
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temporary table</caption><thead align="left"><tr><th align="center" valign="bottom" width="25%" id="d0e76">Old node</th>
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<th align="center" valign="bottom" width="25%" id="d0e78">New node</th>
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<th align="left" valign="bottom" width="25%" id="d0e80">DEPTNAME</th>
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<th align="center" valign="bottom" width="25%" id="d0e82">ADMRDEPT (New partitioning key)</th>
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</tr>
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</thead>
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<tbody><tr><td align="center" valign="top" width="25%" headers="d0e76 ">SYSA</td>
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<td align="center" valign="top" width="25%" headers="d0e78 ">SYSA</td>
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<td align="left" valign="top" width="25%" headers="d0e80 ">Support services</td>
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<td align="center" valign="top" width="25%" headers="d0e82 ">A00</td>
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</tr>
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<tr><td align="center" valign="top" width="25%" headers="d0e76 ">SYSB</td>
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<td align="center" valign="top" width="25%" headers="d0e78 ">SYSA</td>
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<td align="left" valign="top" width="25%" headers="d0e80 ">Planning</td>
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<td align="center" valign="top" width="25%" headers="d0e82 ">A00</td>
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</tr>
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<tr><td align="center" valign="top" width="25%" headers="d0e76 ">SYSC</td>
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<td align="center" valign="top" width="25%" headers="d0e78 ">SYSC</td>
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<td align="left" valign="top" width="25%" headers="d0e80 ">Accounting</td>
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<td align="center" valign="top" width="25%" headers="d0e82 ">B00</td>
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</tr>
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<tr><td align="center" valign="top" width="25%" headers="d0e76 ">SYSA</td>
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<td align="center" valign="top" width="25%" headers="d0e78 ">SYSC</td>
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<td align="left" valign="top" width="25%" headers="d0e80 ">Programming</td>
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<td align="center" valign="top" width="25%" headers="d0e82 ">B00</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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<p>This temporary table is joined to EMPLOYEE. The join works because
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ADMRDEPT is partition compatible with WORKDEPT.</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. EMPLOYEE
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joined table</caption><thead align="left"><tr><th align="left" valign="bottom" width="33.33333333333333%" id="d0e132">DEPTNAME</th>
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<th align="left" valign="bottom" width="33.33333333333333%" id="d0e134">FIRSTNME</th>
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<th align="left" valign="bottom" width="33.33333333333333%" id="d0e136">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="d0e132 ">Support services</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e134 ">Christine</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e136 ">Haas</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e132 ">Planning</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e134 ">Christine</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e136 ">Haas</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e132 ">Accounting</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e134 ">Michael</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e136 ">Thompson</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e132 ">Programming</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e134 ">Michael</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e136 ">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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