69 lines
4.1 KiB
HTML
69 lines
4.1 KiB
HTML
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<meta name="DC.Title" content="View composite implementation" />
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<meta name="abstract" content="The view composite implementation takes the query select statement and combines it with the select statement of the view to generate a new query. The new, combined select statement query is then run directly against the underlying base tables." />
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<meta name="description" content="The view composite implementation takes the query select statement and combines it with the select statement of the view to generate a new query. The new, combined select statement query is then run directly against the underlying base tables." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>View composite implementation</title>
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</head>
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<body id="viewcomposite"><a name="viewcomposite"><!-- --></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">View composite implementation</h1>
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<div><p>The view composite implementation takes the query select statement
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and combines it with the select statement of the view to generate a new query.
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The new, combined select statement query is then run directly against the
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underlying base tables.</p>
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<div class="section"><p>This single, composite statement is the preferred implementation
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for queries containing views, since it requires only a single pass of the
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data.</p>
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<p>See the following examples:</p>
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</div>
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<div class="example"> <pre><strong>CREATE VIEW</strong> D21EMPL <strong>AS</strong>
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<strong>SELECT</strong> * <strong>FROM</strong> CORPDATA.EMPLOYEE
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<strong>WHERE</strong> WORKDEPT='D21'</pre>
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</div>
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<div class="section"><p>Using SQL: </p>
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<pre> <strong>SELECT</strong> LASTNAME, FIRSTNME, SALARY
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<strong>FROM</strong> D21EMPL
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<strong>WHERE</strong> JOB='CLERK' </pre>
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</div>
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<div class="section"><p>The query optimizer will generate a new query that looks like
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the following example: </p>
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<pre><strong>SELECT</strong> LASTNAME, FIRSTNME, SALARY
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<strong>FROM</strong> CORPDATA.EMPLOYEE
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<strong>WHERE</strong> WORKDEPT='D21' <strong>AND</strong> JOB='CLERK' </pre>
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<p>The query
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contains the columns selected by the user's query, the base tables referenced
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in the query, and the selection from both the view and the user's query.</p>
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<div class="note"><span class="notetitle">Note:</span> The
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new composite query that the query optimizer generates is not visible to users.
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Only the original query against the view will be seen by users and database
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performance tools.</div>
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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="viewopt.htm" title="Views, derived tables (nested table expressions or NTEs), and common table expressions (CTEs) are implemented by the query optimizer using one of two methods.">View implementation</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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