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<h1 class="topictitle1">Repartitioned join with DB2<sup>®</sup> Multisystem</h1>
<div><p>In a repartitioned join, the partitioning keys of the files are
not used as the join fields.</p>
<div class="section"><p>Records of both files must be moved by hashing the join field
values of each of the files. Because neither of the files' partitioning key
fields are included in the join criteria, the files must be repartitioned
by hashing on a new partitioning key that includes one or more of the join
fields. This method is valid only for equijoin queries. </p>
<p>SQL statement:</p>
<pre> SELECT DEPTNAME, FIRSTNME, LASTNAME
FROM DEPARTMENT, EMPLOYEE
WHERE MGRNO = EMPNO</pre>
<p>OPNQRYF command:</p>
<pre> OPNQRYF FILE((DEPARTMENT) (EMPLOYEE))
FORMAT(JOINFMT)
JFLD((MGRNO EMPNO *EQ))</pre>
<p>In this example,
the data must be redistributed because neither MGRNO nor EMPNO is a partitioning
key.</p>
<p>Data from DEPARTMENT is redistributed:</p>
<table cellpadding="4" cellspacing="0" border="1" class="tableborder"><tr><td>
<table cellpadding="4" cellspacing="0" summary="" border="0"><caption>Table 1. Redistributed
DEPARTMENT data</caption><thead align="left"><tr><th align="center" valign="bottom" width="25%" id="d0e76">Old node</th>
<th align="center" valign="bottom" width="25%" id="d0e78">New node</th>
<th align="left" valign="bottom" width="25%" id="d0e80">DEPTNAME</th>
<th align="center" valign="bottom" width="25%" id="d0e82">MGRNO (New partitioning key)</th>
</tr>
</thead>
<tbody><tr><td align="center" valign="top" width="25%" headers="d0e76 ">SYSA</td>
<td align="center" valign="top" width="25%" headers="d0e78 ">SYSB</td>
<td align="left" valign="top" width="25%" headers="d0e80 ">Support services</td>
<td align="center" valign="top" width="25%" headers="d0e82 ">000010</td>
</tr>
<tr><td align="center" valign="top" width="25%" headers="d0e76 ">SYSB</td>
<td align="center" valign="top" width="25%" headers="d0e78 ">SYSB</td>
<td align="left" valign="top" width="25%" headers="d0e80 ">Planning</td>
<td align="center" valign="top" width="25%" headers="d0e82 ">000010</td>
</tr>
<tr><td align="center" valign="top" width="25%" headers="d0e76 ">SYSC</td>
<td align="center" valign="top" width="25%" headers="d0e78 ">SYSC</td>
<td align="left" valign="top" width="25%" headers="d0e80 ">Accounting</td>
<td align="center" valign="top" width="25%" headers="d0e82 ">000050</td>
</tr>
<tr><td align="center" valign="top" width="25%" headers="d0e76 ">SYSA</td>
<td align="center" valign="top" width="25%" headers="d0e78 ">SYSC</td>
<td align="left" valign="top" width="25%" headers="d0e80 ">Programming</td>
<td align="center" valign="top" width="25%" headers="d0e82 ">000050</td>
</tr>
</tbody>
</table>
</td></tr></table>
<p>Data from EMPLOYEE is redistributed:</p>
<table cellpadding="4" cellspacing="0" border="1" class="tableborder"><tr><td>
<table cellpadding="4" cellspacing="0" summary="" border="0"><caption>Table 2. Redistributed
EMPLOYEE data</caption><thead align="left"><tr><th align="center" valign="bottom" width="20%" id="d0e134">Old node</th>
<th align="center" valign="bottom" width="20%" id="d0e136">New node</th>
<th align="left" valign="bottom" width="20%" id="d0e138">FIRSTNME</th>
<th align="left" valign="bottom" width="20%" id="d0e140">LASTNAME</th>
<th align="center" valign="bottom" width="20%" id="d0e142">EMPNO (New partitioning key)</th>
</tr>
</thead>
<tbody><tr><td align="center" valign="top" width="20%" headers="d0e134 ">SYSA</td>
<td align="center" valign="top" width="20%" headers="d0e136 ">SYSB</td>
<td align="left" valign="top" width="20%" headers="d0e138 ">Christine</td>
<td align="left" valign="top" width="20%" headers="d0e140 ">Haas</td>
<td align="center" valign="top" width="20%" headers="d0e142 ">000010</td>
</tr>
<tr><td align="center" valign="top" width="20%" headers="d0e134 ">SYSA</td>
<td align="center" valign="top" width="20%" headers="d0e136 ">SYSC</td>
<td align="left" valign="top" width="20%" headers="d0e138 ">Sally</td>
<td align="left" valign="top" width="20%" headers="d0e140 ">Kwan</td>
<td align="center" valign="top" width="20%" headers="d0e142 ">000020</td>
</tr>
<tr><td align="center" valign="top" width="20%" headers="d0e134 ">SYSB</td>
<td align="center" valign="top" width="20%" headers="d0e136 ">SYSA</td>
<td align="left" valign="top" width="20%" headers="d0e138 ">John</td>
<td align="left" valign="top" width="20%" headers="d0e140 ">Geyer</td>
<td align="center" valign="top" width="20%" headers="d0e142 ">000030</td>
</tr>
<tr><td align="center" valign="top" width="20%" headers="d0e134 ">SYSB</td>
<td align="center" valign="top" width="20%" headers="d0e136 ">SYSB</td>
<td align="left" valign="top" width="20%" headers="d0e138 ">Irving</td>
<td align="left" valign="top" width="20%" headers="d0e140 ">Stern</td>
<td align="center" valign="top" width="20%" headers="d0e142 ">000040</td>
</tr>
<tr><td align="center" valign="top" width="20%" headers="d0e134 ">SYSC</td>
<td align="center" valign="top" width="20%" headers="d0e136 ">SYSC</td>
<td align="left" valign="top" width="20%" headers="d0e138 ">Michael</td>
<td align="left" valign="top" width="20%" headers="d0e140 ">Thompson</td>
<td align="center" valign="top" width="20%" headers="d0e142 ">000050</td>
</tr>
<tr><td align="center" valign="top" width="20%" headers="d0e134 ">SYSC</td>
<td align="center" valign="top" width="20%" headers="d0e136 ">SYSA</td>
<td align="left" valign="top" width="20%" headers="d0e138 ">Eileen</td>
<td align="left" valign="top" width="20%" headers="d0e140 ">Henderson</td>
<td align="center" valign="top" width="20%" headers="d0e142 ">000060</td>
</tr>
<tr><td align="center" valign="top" width="20%" headers="d0e134 ">SYSA</td>
<td align="center" valign="top" width="20%" headers="d0e136 ">SYSB</td>
<td align="left" valign="top" width="20%" headers="d0e138 ">Jennifer</td>
<td align="left" valign="top" width="20%" headers="d0e140 ">Lutz</td>
<td align="center" valign="top" width="20%" headers="d0e142 ">000070</td>
</tr>
<tr><td align="center" valign="top" width="20%" headers="d0e134 ">SYSA</td>
<td align="center" valign="top" width="20%" headers="d0e136 ">SYSC</td>
<td align="left" valign="top" width="20%" headers="d0e138 ">David</td>
<td align="left" valign="top" width="20%" headers="d0e140 ">White</td>
<td align="center" valign="top" width="20%" headers="d0e142 ">000080</td>
</tr>
</tbody>
</table>
</td></tr></table>
<p>Records returned by this query:</p>
<table cellpadding="4" cellspacing="0" border="1" class="tableborder"><tr><td>
<table cellpadding="4" cellspacing="0" summary="" border="0"><caption>Table 3. Display
of the query results</caption><thead align="left"><tr><th align="left" valign="bottom" width="33.33333333333333%" id="d0e244">DEPTNAME</th>
<th align="left" valign="bottom" width="33.33333333333333%" id="d0e246">FIRSTNME</th>
<th align="left" valign="bottom" width="33.33333333333333%" id="d0e248">LASTNAME</th>
</tr>
</thead>
<tbody><tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e244 ">Support services</td>
<td align="left" valign="top" width="33.33333333333333%" headers="d0e246 ">Christine</td>
<td align="left" valign="top" width="33.33333333333333%" headers="d0e248 ">Haas</td>
</tr>
<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e244 ">Planning</td>
<td align="left" valign="top" width="33.33333333333333%" headers="d0e246 ">Christine</td>
<td align="left" valign="top" width="33.33333333333333%" headers="d0e248 ">Haas</td>
</tr>
<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e244 ">Accounting</td>
<td align="left" valign="top" width="33.33333333333333%" headers="d0e246 ">Michael</td>
<td align="left" valign="top" width="33.33333333333333%" headers="d0e248 ">Thompson</td>
</tr>
<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e244 ">Programming</td>
<td align="left" valign="top" width="33.33333333333333%" headers="d0e246 ">Michael</td>
<td align="left" valign="top" width="33.33333333333333%" headers="d0e248 ">Thompson</td>
</tr>
</tbody>
</table>
</td></tr></table>
</div>
</div>
<div>
<div class="familylinks">
<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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