69 lines
4.1 KiB
HTML
69 lines
4.1 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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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Usage notes on subqueries" />
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<meta name="abstract" content="When using subqueries, you should be aware of these usage notes." />
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<meta name="description" content="When using subqueries, you should be aware of these usage notes." />
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<meta name="DC.subject" content="subquery, notes on using" />
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<meta name="keywords" content="subquery, notes on using" />
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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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<!-- All rights reserved. Licensed Materials Property of IBM -->
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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>Usage notes on subqueries</title>
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</head>
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<body id="rbafysubquerynotes"><a name="rbafysubquerynotes"><!-- --></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">Usage notes on subqueries</h1>
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<div><p>When using subqueries, you should be aware of these usage notes.</p>
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<div class="section"> <ol><li>When nesting SELECT statements, you can use as many as you need to satisfy
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your requirements (1 to 255 subqueries), although performance is slower for
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each additional subquery.</li>
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<li><img src="./delta.gif" alt="Start of change" />For predicates using the keywords ALL, ANY, SOME, or
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EXISTS, the number of rows returned from the subquery can vary from zero to
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many. For all other subqueries, the number of rows returned must be zero or
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one.<img src="./deltaend.gif" alt="End of change" /></li>
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<li><img src="./delta.gif" alt="Start of change" />For the following predicates, a row fullselect can be
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used for the subquery. This means that the subquery can return more than one
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value for a row.<ul><li>Basic predicate with equal or not equal comparisons</li>
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<li>Quantified predicates using =ANY, =ALL, and =SOME</li>
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<li>IN and NOT IN predicates</li>
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</ul>
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If a row fullselect is used:<ul><li>The select list must not contain SELECT *. Explicit values must be specified.</li>
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<li>A row fullselect must be compared to a row expression. A row expression
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is a list of values enclosed in parentheses. There must be the same number
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of values returned from the subquery as there are in the row expression.</li>
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<li>The row expression for an IN or NOT IN predicate cannot contain an untyped
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parameter marker. Use CAST to supply a result data type for these parameter
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markers.</li>
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<li>The subquery cannot contain UNION, EXCEPT, or INTERSECT or a
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correlated reference.</li>
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</ul>
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<img src="./deltaend.gif" alt="End of change" /></li>
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<li><img src="./delta.gif" alt="Start of change" />A subquery cannot include the ORDER BY, FOR READ ONLY,
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FETCH FIRST <em>n</em> ROWS, UPDATE, or OPTIMIZE clauses.<img src="./deltaend.gif" alt="End of change" /></li>
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</ol>
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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="rbafysubq.htm" title="Subqueries can help you to further refine your search conditions.">Subqueries in SELECT statements</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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