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210 lines
9.1 KiB
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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>db get</title>
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<link rel="stylesheet" href="apiReference.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 TCL API Reference" />
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<link rel="up" href="tclapi.html" title="Chapter 1. Berkeley DB Tcl APIs" />
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<link rel="prev" href="db_del.html" title="db del" />
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<link rel="next" href="db_get_join.html" title="db get_join" />
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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 11.2.5.2</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"><span xmlns="http://www.w3.org/1999/xhtml" class="emphasis"><em>db</em></span> get</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="db_del.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 1.
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Berkeley DB Tcl APIs
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="db_get_join.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="db_get"></a><span class="emphasis"><em>db</em></span> get</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">db get
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[-consume]
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[-consume_wait]
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[-glob]
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[-partial {doff dlen}]
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[-recno]
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[-rmw]
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[-txn txnid]
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key
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db get
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-get_both
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[-partial {doff dlen}]
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[-rmw]
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[-txn txnid]
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key data </pre>
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<p>
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The <span class="emphasis"><em>db</em></span> <span class="bold"><strong>get</strong></span>
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command returns key/data pairs from the database.
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</p>
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<p>
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In the presence of duplicate key values, <span class="emphasis"><em>db</em></span>
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<span class="bold"><strong>get</strong></span> will return all duplicate items.
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Duplicates are sorted by insert order except where this order has been
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overridden by cursor operations.
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</p>
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<p>
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The options are as follows:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<span class="bold"><strong>-consume</strong></span>
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</p>
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<p>
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Return the record number and data from the available record closest to
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the head of the queue, and delete the record. The cursor will be
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positioned on the deleted record. A record is available if it is not
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deleted and is not currently locked. The underlying database must be
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of type Queue for <span class="bold"><strong>-consume</strong></span> to be
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specified.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>-consume_wait</strong></span>
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</p>
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<p>
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The same as the <span class="bold"><strong>-consume</strong></span> flag except
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that if the Queue database is empty, the thread of control will wait
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until there is data in the queue before returning. The underlying
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database must be of type Queue for <span class="bold"><strong>-consume_wait</strong></span> to be specified.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>-get_both key data</strong></span>
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</p>
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<p>
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Retrieve the key/data pair only if both the key and data match the
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arguments.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>-glob</strong></span>
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</p>
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<p>
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Return all keys matching the given key, where the key is a simple
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wildcard pattern. Where it is used, it replaces the use of the key
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with the given pattern of a set of keys. Any characters after the
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wildcard character are ignored. For example, in a database of last
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names, the command "db0 get Jones" will return all occurrences of
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"Jones" in the database, and the command "db0 get -glob Jo*" will
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return both "Jones" and "Johnson" from the database. The command "db0
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get -glob *" will return all of the key/data pairs in the database.
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This option only works on databases using the Btree access method.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>-partial {doff dlen}</strong></span>
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</p>
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<p>
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The <span class="bold"><strong>dlen</strong></span> bytes starting <span class="bold"><strong>doff</strong></span> bytes from the beginning of the retrieved
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data record are returned as if they comprised the entire record. If
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any or all of the specified bytes do not exist in the record, the
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command is successful and any existing bytes are returned.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>-recno</strong></span>
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</p>
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<p>
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Retrieve the specified numbered key/data pair from a database. For
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<span class="bold"><strong>-recno</strong></span> to be specified, the specified
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key must be a record number; and the underlying database must be of
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type Recno or Queue, or of type Btree that was created with the
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<span class="bold"><strong>-recnum</strong></span> option.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>-rmw</strong></span>
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</p>
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<p>
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Acquire write locks instead of read locks when doing the retrieval.
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Setting this flag may decrease the likelihood of deadlock during a
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read-modify-write cycle by immediately acquiring the write lock during
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the read part of the cycle so that another thread of control acquiring
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a read lock for the same item, in its own read-modify-write cycle,
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will not result in deadlock.
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</p>
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<p>
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Because the <span class="emphasis"><em>db</em></span> <span class="bold"><strong>get</strong></span> command will not hold locks across Berkeley
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DB interface calls in nontransactional environments, the <span class="bold"><strong>-rmw</strong></span> argument to the <span class="emphasis"><em>db</em></span>
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<span class="bold"><strong>get</strong></span> call is only meaningful in the
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presence of transactions.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>-txn txnid</strong></span>
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</p>
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<p>
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If the operation is part of an application-specified transaction, the
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<span class="bold"><strong>txnid</strong></span> parameter is a transaction
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handle returned from <span class="emphasis"><em>env</em></span> <span class="bold"><strong>txn</strong></span>. If no transaction handle is specified,
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but the operation occurs in a transactional database, the operation
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will be implicitly transaction protected.
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</p>
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</li>
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</ul>
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</div>
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<p>
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If the underlying database is a Queue or Recno database, the given key
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will be interpreted by Tcl as an integer. For all other database
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types, the key is interpreted by Tcl as a byte array, unless indicated
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by a given option.
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</p>
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<p>
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A list of key/data pairs is returned. In the error case that no
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matching key exists, an empty list is returned. In all other cases, a
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Tcl error is thrown.
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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="db_del.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="tclapi.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="db_get_join.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"><span class="emphasis"><em>db</em></span> del </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"> <span class="emphasis"><em>db</em></span> get_join</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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