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https://github.com/berkeleydb/je.git
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215 lines
7.4 KiB
HTML
215 lines
7.4 KiB
HTML
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Chapter 9. Using Cursors</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
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<link rel="up" href="baseapi.html" title="Part II. Programming with the Base API" />
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<link rel="prev" href="dbtUsage.html" title="Database Record Example" />
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<link rel="next" href="Positioning.html" title="Getting Records Using the Cursor" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.2.7.5</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Chapter 9. Using Cursors</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbtUsage.html">Prev</a> </td>
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<th width="60%" align="center">Part II. Programming with the Base API</th>
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<td width="20%" align="right"> <a accesskey="n" href="Positioning.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="chapter" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title"><a id="Cursors"></a>Chapter 9. Using Cursors</h2>
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</div>
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</div>
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</div>
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<div class="toc">
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<p>
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<b>Table of Contents</b>
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</p>
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<dl>
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<dt>
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<span class="sect1">
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<a href="Cursors.html#openCursor">Opening and Closing Cursors</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="Positioning.html">Getting Records Using the Cursor</a>
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</span>
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</dt>
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<dd>
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<dl>
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<dt>
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<span class="sect2">
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<a href="Positioning.html#diskorderedcursors">Disk Ordered Cursors</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="Positioning.html#cursorsearch">Searching for Records</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="Positioning.html#getdups">Working with Duplicate Records</a>
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</span>
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</dt>
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</dl>
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</dd>
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<dt>
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<span class="sect1">
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<a href="PutEntryWCursor.html">Putting Records Using Cursors</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="DeleteEntryWCursor.html">Deleting Records Using Cursors</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="ReplacingEntryWCursor.html">Replacing Records Using Cursors</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="cursorUsage.html">Cursor Example</a>
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</span>
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</dt>
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</dl>
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</div>
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<p>
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Cursors provide a mechanism by which you can iterate over the records in a
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database. Using cursors, you can get, put, and delete database records. If
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a database allows duplicate records, then cursors are
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<span>the only mechanism by
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which you can access anything other than the first duplicate for a given
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key.</span>
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</p>
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<p>
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This chapter introduces cursors. It explains how to open and close them, how
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to use them to modify databases, and how to use them with duplicate records.
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</p>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="openCursor"></a>Opening and Closing Cursors</h2>
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</div>
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</div>
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</div>
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<p>
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To use a cursor, you must open it using the <code class="methodname">Database.openCursor()</code>
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method. When you open a
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cursor, you can optionally pass it a <code class="classname">CursorConfig</code>
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object to set cursor properties.
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<span>
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The cursor properties that you can set allows you to
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determine whether the cursor will perform committed or
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uncommitted reads. See the
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<em class="citetitle">Berkeley DB, Java Edition Getting Started with Transaction Processing</em> guide for more
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information.
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</span>
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</p>
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<p>For example:</p>
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<a id="je_cursor1"></a>
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<pre class="programlisting">package je.gettingStarted;
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import com.sleepycat.je.Cursor;
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import com.sleepycat.je.Database;
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import com.sleepycat.je.DatabaseException;
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import com.sleepycat.je.Environment;
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import java.io.File;
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...
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Environment myDbEnvironment = null;
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Database myDatabase = null;
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Cursor myCursor = null;
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try {
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myDbEnvironment = new Environment(new File("/export/dbEnv"), null);
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myDatabase = myDbEnvironment.openDatabase(null, "myDB", null);
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myCursor = myDatabase.openCursor(null, null);
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} catch (DatabaseException dbe) {
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// Exception handling goes here ...
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}</pre>
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<p>
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To close the cursor, call the <code class="methodname">Cursor.close()</code>
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method. Note that if you close a database that has cursors open in it,
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then it will throw an exception and close any open cursors for you.
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For best results, close your cursors from within a
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<code class="literal">finally</code> block. However, it is recommended that you always close all cursor handles immediately after their use to ensure concurrency and to release resources such as page locks.
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<span></span>
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</p>
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<a id="je_cursor2"></a>
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<pre class="programlisting">package je.gettingStarted;
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import com.sleepycat.je.Cursor;
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import com.sleepycat.je.Database;
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import com.sleepycat.je.Environment;
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...
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try {
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...
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} catch ... {
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} finally {
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try {
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if (myCursor != null) {
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myCursor.close();
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}
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if (myDatabase != null) {
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myDatabase.close();
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}
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if (myDbEnvironment != null) {
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myDbEnvironment.close();
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}
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} catch(DatabaseException dbe) {
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System.err.println("Error in close: " + dbe.toString());
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}
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} </pre>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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|||
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<td width="40%" align="left"><a accesskey="p" href="dbtUsage.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="baseapi.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="Positioning.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Database Record Example </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Getting Records Using the Cursor</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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