66 lines
3.7 KiB
HTML
66 lines
3.7 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="Check constraint optimization" />
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<meta name="abstract" content="The optimizer uses check constraints (either user-added or the implicit check constraints added for the partition key) to reduce the partitions examined." />
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<meta name="description" content="The optimizer uses check constraints (either user-added or the implicit check constraints added for the partition key) to reduce the partitions examined." />
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<meta name="DC.Relation" scheme="URI" content="rzaf3sqept.htm" />
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<meta name="DC.Relation" scheme="URI" content="creatept.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.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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<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>Check constraint optimization</title>
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</head>
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<body id="rzaf3ptcheck"><a name="rzaf3ptcheck"><!-- --></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">Check constraint optimization</h1>
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<div><p>The optimizer uses check constraints (either user-added or the
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implicit check constraints added for the partition key) to reduce the partitions
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examined.</p>
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<div class="section"><p>For additional information about the implicitly added partitioning
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key constraints see Creating partitioned tables. In the following example,
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assume that PAYROLL is partitioned by range:</p>
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<pre>SELECT LASTNAME, SALARY
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FROM PRODLIB.PAYROLL
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WHERE EMPNUM = :hv1</pre>
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<p>The optimizer adds new predicates
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to each partition in the table:</p>
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<pre>SELECT LASTNAME, SALARY FROM
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(SELECT LASTNAME, SALARY FROM PRODLB.PAYROLL(PART00001)
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WHERE EMPNUM=:hv1 AND :hv1 <= 500
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UNION ALL
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SELECT LASTNAME, SALARY FROM PRODLB.PAYROLL(PART00002)
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WHERE EMPNUM=:hv1 AND :hv1 >= 501 AND :hv1 <=1000
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UNION ALL
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SELECT LASTNAME, SALARY FROM PRODLB.PAYROLL(PART00003)
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WHERE EMPNUM=:hv1 AND (:hv1 IS NULL OR :hv1 >= 1001))
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X (LASTNAME, SALARY)</pre>
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<p>If the value of hv1 is
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603, then only the rows of partition PART00002 are examined.</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="rzaf3sqept.htm" title="The SQL Query Engine (SQE) provides targeted optimization for partitioned tables using dynamic partition expansion optimization.">Queries using SQL Query Engine</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="creatept.htm" title="New partitioned tables can be created using the CREATE TABLE statement.">Creation of partitioned tables</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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