102 lines
5.1 KiB
HTML
102 lines
5.1 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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<meta name="DC.Title" content="MQT examples" />
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<meta name="abstract" content="The following are examples of using MQTs." />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>MQT examples</title>
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</head>
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<body id="rzajqmqtexample"><a name="rzajqmqtexample"><!-- --></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">MQT examples</h1>
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<div><p>The following are examples of using MQTs.</p>
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<div class="section"><h4 class="sectiontitle">Example 1</h4><div class="p">The first example is a query that returns
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information about employees whose job is DESIGNER. The original query looks
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like this: <pre>Q1: SELECT D.deptname, D.location, E.firstnme, E.lastname, E.salary+E.comm+E.bonus as total_sal
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FROM Department D, Employee E
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WHERE D.deptno=E.workdept
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AND E.job = 'DESIGNER'</pre>
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</div>
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</div>
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<div class="section"><div class="p">Create a table, MQT1, that uses this query: <pre>CREATE TABLE MQT1
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AS (SELECT D.deptname, D.location, E.firstnme, E.lastname, E.salary, E.comm, E.bonus, E.job
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FROM Department D, Employee E
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WHERE D.deptno=E.workdept)
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DATA INITIALLY IMMEDIATE REFRESH DEFERRED
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ENABLE QUERY OPTIMIZATION
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MAINTAINED BY USER</pre>
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</div>
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</div>
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<div class="section"><div class="p">Resulting new query after replacing the specified tables with
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the MQT. <pre>SELECT M.deptname, M.location, M.firstnme, M.lastname, M.salary+M.comm+M.bonus as total_sal
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FROM MQT1 M
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WHERE M.job = 'DESIGNER'</pre>
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</div>
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</div>
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<div class="section"><p>In this query, the MQT matches part of the user's query. The
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MQT is placed in the FROM clause and replaces tables DEPARTMENT and EMPLOYEE.
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Any remaining selection not done by the MQT query (M.job= 'DESIGNER') is
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done to remove the extra rows and the result expression, M.salary+M.comm+M.bonus,
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is calculated. Note that JOB must be in the select-list of the MQT so that
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the additional selection can be performed.</p>
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</div>
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<div class="section"><p>Visual Explain diagram of the query when using the MQT:<br /><img src="rzajq554.gif" alt="" /><br /></p>
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</div>
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<div class="section"><h4 class="sectiontitle">Example 2</h4><div class="p">Get the total salary for all departments
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that are located in 'NY'. The original query looks like this: <pre>SELECT D.deptname, sum(E.salary)
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FROM DEPARTMENT D, EMPLOYEE E
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WHERE D.deptno=E.workdept AND D.location = 'NY'
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GROUP BY D.deptname</pre>
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</div>
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</div>
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<div class="section"><div class="p">Create a table, MQT2, that uses this query: <pre>CREATE TABLE MQT2
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AS (SELECT D.deptname, D.location, sum(E.salary) as sum_sal
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FROM DEPARTMENT D, EMPLOYEE E
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WHERE D.deptno=E.workdept
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GROUP BY D.Deptname, D.location)
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DATA INITIALLY IMMEDIATE REFRESH DEFERRED
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ENABLE QUERY OPTIMIZATION
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MAINTAINED BY USER</pre>
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</div>
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</div>
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<div class="section"><div class="p">Resulting new query after replacing the specified tables with
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the MQT: <pre>SELECT M.deptname, sum(M.sum_sal)
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FROM MQT2 M
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WHERE M.location = 'NY'
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GROUP BY M.deptname</pre>
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</div>
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</div>
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<div class="section"><p>Since the MQT may potentially produce more groups
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than the original query, the final resulting query must group again and SUM
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the results to return the correct answer. Also the selection M.location='NY'
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must be part of the new query.</p>
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</div>
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<div class="section"><p>Visual Explain diagram of the query when using the MQT:<br /><img src="rzajq553.gif" alt="" /><br /></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="rzajqmqt.htm" title="Materialized query tables (MQTs) (also referred to as automatic summary tables or materialized views) can provide performance enhancements for queries.">Materialized query table optimization</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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