51 lines
3.9 KiB
HTML
51 lines
3.9 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="Avoid arithmetic expressions" />
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<meta name="abstract" content="Do not use an arithmetic expression as an operand to be compared to a column in a row selection predicate. The optimizer does not use an index on a column that is being compared to an arithmetic expression. While this may not cause an index over the column to become unusable, it will prevent any estimates and possibly the use of index scan-key positioning on the index. The primary thing that is lost is the ability to use and extract any statistics that might be useful in the optimization of the query." />
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<meta name="description" content="Do not use an arithmetic expression as an operand to be compared to a column in a row selection predicate. The optimizer does not use an index on a column that is being compared to an arithmetic expression. While this may not cause an index over the column to become unusable, it will prevent any estimates and possibly the use of index scan-key positioning on the index. The primary thing that is lost is the ability to use and extract any statistics that might be useful in the optimization of the query." />
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<meta name="DC.Relation" scheme="URI" content="rzajqeffectindex.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>Avoid arithmetic expressions</title>
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</head>
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<body id="avoidarithexp"><a name="avoidarithexp"><!-- --></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">Avoid arithmetic expressions</h1>
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<div><p>Do not use an arithmetic expression as an operand to be compared
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to a column in a row selection predicate. The optimizer does not use an index
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on a column that is being compared to an arithmetic expression. While this
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may not cause an index over the column to become unusable, it will prevent
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any estimates and possibly the use of index scan-key positioning on the index.
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The primary thing that is lost is the ability to use and extract any statistics
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that might be useful in the optimization of the query.</p>
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<div class="section"><p>For example, when using SQL, specify the following: </p>
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<pre>… <strong>WHERE</strong> SALARY > 16500 </pre>
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</div>
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<div class="section"><p>instead of </p>
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<pre>… <strong>WHERE</strong> SALARY > 15000*1.1 </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="rzajqeffectindex.htm" title="The following topics provide suggestions that will help you to design code which allows DB2 Universal Database for iSeries to take advantage of available indexes:">Coding for effective indexes</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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