mirror of
https://github.com/yasuhirokimura/db18
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Yasuhiro KIMURA
111 lines
4.3 KiB
HTML
111 lines
4.3 KiB
HTML
<?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>Retrieving records</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="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="am.html" title="Chapter 3. Access Method Operations" />
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<link rel="prev" href="am_partition.html" title="Partitioning databases" />
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<link rel="next" href="am_put.html" title="Storing records" />
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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 18.1.40</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">Retrieving records</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="am_partition.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 3. Access Method Operations </th>
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<td width="20%" align="right"> <a accesskey="n" href="am_put.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="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="am_get"></a>Retrieving records</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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The <a href="../api_reference/C/dbget.html" class="olink">DB->get()</a> method retrieves records from the database. In
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general, <a href="../api_reference/C/dbget.html" class="olink">DB->get()</a> takes a key and returns the associated data
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from the database.
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</p>
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<p>
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There are a few flags that you can set to customize
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retrieval:
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</p>
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<div class="variablelist">
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<dl>
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<dt>
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<span class="term">
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<a href="../api_reference/C/dbget.html#get_DB_GET_BOTH" class="olink">DB_GET_BOTH</a>
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</span>
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</dt>
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<dd>
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Search for a matching key and data item, that
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is, only return success if both the key and the data
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items match those stored in the database.
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</dd>
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<dt>
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<span class="term">
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<a href="../api_reference/C/dbcget.html#dbcget_DB_RMW" class="olink">DB_RMW</a>
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</span>
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</dt>
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<dd>
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Read-modify-write: acquire write locks instead
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of read locks during retrieval. This can enhance
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performance in threaded applications by reducing the
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chance of deadlock.
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</dd>
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<dt>
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<span class="term">
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<a href="../api_reference/C/dbget.html#dbget_DB_SET_RECNO" class="olink">DB_SET_RECNO</a>
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</span>
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</dt>
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<dd>
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If the underlying database is a Btree, and was
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configured so that it is possible to search it by
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logical record number, retrieve a specific
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record.
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</dd>
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</dl>
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</div>
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<p>
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If the database has been configured to support duplicate
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records, <a href="../api_reference/C/dbget.html" class="olink">DB->get()</a> will always return the first data item in the
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duplicate set.
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</p>
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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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<td width="40%" align="left"><a accesskey="p" href="am_partition.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="am.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="am_put.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">Partitioning databases </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"> Storing records</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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