2011-09-13 17:44:24 +00:00
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<title>DB->join()</title>
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<p>Library Version 11.2.5.2</p>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">DB->join()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbget_type.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2.
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The DB Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="dbkey_range.html">Next</a></td>
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<div>
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<h2 class="title" style="clear: both"><a id="dbjoin"></a>DB->join()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db.h>
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int
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DB->join(DB *primary,
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DBC **curslist, DBC **dbcp, u_int32_t flags); </pre>
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<p>
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The <code class="methodname">DB->join()</code> method creates a specialized join cursor for use in
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performing equality or natural joins on secondary indices. For
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information on how to organize your data to use this functionality,
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see <a href="../../programmer_reference/am_cursor.html#am_join" class="olink">Equality join</a>.
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</p>
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<p>
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The <code class="methodname">DB->join()</code> method is called using the
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<a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a> handle of the primary
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database.
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</p>
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<p>
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The join cursor supports only the <a class="xref" href="dbcget.html" title="DBcursor->get()">DBcursor->get()</a> and
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<a class="xref" href="dbcclose.html" title="DBcursor->close()">DBcursor->close()</a> cursor functions:
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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> <a class="xref" href="dbcget.html" title="DBcursor->get()">DBcursor->get()</a> </strong></span>
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</p>
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<p>
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Iterates over the values associated with the keys to which each item
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in <span class="bold"><strong>curslist</strong></span> was initialized. Any
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data value that appears in all items specified by the <span class="bold"><strong>curslist</strong></span> parameter is then used as a key into
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the <span class="bold"><strong>primary</strong></span>, and the key/data pair
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found in the <span class="bold"><strong>primary</strong></span> is returned. The
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<span class="bold"><strong>flags</strong></span> parameter must be set to 0 or
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the following value:
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</p>
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<div class="itemizedlist">
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<ul type="circle">
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<li>
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<p>
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<span class="bold"><strong><code class="literal">DB_JOIN_ITEM</code></strong></span>
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</p>
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<p>
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Do not use the data value found in all the cursors as a lookup key for
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the <span class="bold"><strong>primary</strong></span>, but simply return it in
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the key parameter instead. The data parameter is left unchanged.
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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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In addition, the following flag may be set by bitwise inclusively
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<span class="bold"><strong>OR</strong></span>'ing it into the <span class="bold"><strong>flags</strong></span> parameter:
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</p>
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<div class="itemizedlist">
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<ul type="circle">
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<li>
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<p>
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<span class="bold"><strong> <code class="literal">DB_READ_UNCOMMITTED</code></strong></span>
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</p>
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<p>
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Configure a transactional join operation to have degree 1 isolation,
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reading modified but not yet committed data. Silently ignored if the
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<a class="link" href="dbopen.html#dbopen_DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a>
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flag was not specified when the underlying database was opened.
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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><code class="literal">DB_RMW</code></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 read, if
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locking is configured. Setting this flag can eliminate deadlock
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during a read-modify-write cycle by 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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</li>
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</ul>
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</div>
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</li>
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<li>
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<p>
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<span class="bold"><strong> <a class="xref" href="dbcclose.html" title="DBcursor->close()">DBcursor->close()</a> </strong></span>
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</p>
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<p>
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Close the returned cursor and release all resources. (Closing the
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cursors in <span class="bold"><strong>curslist</strong></span> is the
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responsibility of the caller.)
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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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The <code class="methodname">DB->join()</code> <span>
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<span>
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method returns a non-zero error value on failure and 0 on success.
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</span>
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</span>
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</p>
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<div class="sect2" 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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3681028"></a>Parameters</h3>
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</div>
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</div>
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</div>
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<div class="sect3" 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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3680967"></a>curslist</h4>
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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 <span class="bold"><strong>curslist</strong></span> parameter contains a
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NULL terminated array of cursors. Each cursor must have been
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initialized to refer to the key on which the underlying database
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should be joined. Typically, this initialization is done by a
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<a class="xref" href="dbcget.html" title="DBcursor->get()">DBcursor->get()</a> call with the
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<a class="link" href="dbcget.html#dbcget_DB_SET">DB_SET</a> flag
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specified. Once the cursors have been passed as part of a <span class="bold"><strong>curslist</strong></span>, they should not be accessed or
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modified until the newly created join cursor has been closed, or else
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inconsistent results may be returned.
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</p>
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<p>
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Joined values are retrieved by doing a sequential iteration over the
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first cursor in the <span class="bold"><strong>curslist</strong></span>
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parameter, and a nested iteration over each secondary cursor in the
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order they are specified in the <span class="bold"><strong>curslist</strong></span> parameter. This requires database
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traversals to search for the current datum in all the cursors after
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the first. For this reason, the best join performance normally
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results from sorting the cursors from the one that refers to the least
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number of data items to the one that refers to the most. By default,
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<code class="methodname">DB->join()</code> does this sort on behalf of its caller.
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</p>
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<p>
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For the returned join cursor to be used in a transaction-protected
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manner, the cursors listed in <span class="bold"><strong>curslist</strong></span> must have been created within the
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context of the same transaction.
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</p>
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</div>
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<div class="sect3" 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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3680809"></a>dbcp</h4>
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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 newly created join cursor is returned in the memory location to
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which <span class="bold"><strong>dbcp</strong></span> refers.
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</p>
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</div>
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<div class="sect3" 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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3681276"></a>flags</h4>
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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 <span class="bold"><strong>flags</strong></span> parameter must be set to 0
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or the following value:
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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><a id="join_DB_JOIN_NOSORT"></a>
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<code class="literal">DB_JOIN_NOSORT</code>
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</p>
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<p>
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Do not sort the cursors based on the number of data items to which
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they refer. If the data are structured so that cursors with many data
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items also share many common elements, higher performance will result
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from listing those cursors before cursors with fewer data items; that
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is, a sort order other than the default. The DB_JOIN_NOSORT flag
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permits applications to perform join optimization prior to calling the
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<code class="methodname">DB->join()</code> method.
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</p>
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</li>
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</ul>
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</div>
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</div>
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</div>
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<div class="sect2" 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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2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3680999"></a>Errors</h3>
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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 <code class="methodname">DB->join()</code> <span>
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<span>
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method may fail and return one of the following non-zero errors:
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</span>
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</span>
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</p>
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<div class="sect3" 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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3680862"></a> DB_REP_HANDLE_DEAD</h4>
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</div>
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</div>
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</div>
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<p>
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When a client synchronizes with the master, it is possible for committed
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transactions to be rolled back. This invalidates all the database and cursor
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handles opened in the replication environment. Once this occurs, an attempt to use
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such a handle will
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return <code class="literal">DB_REP_HANDLE_DEAD</code>.
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The application will need to discard the handle and open a new one in order to
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continue processing.
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</p>
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</div>
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<div class="sect3" 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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3681315"></a>DB_REP_LOCKOUT</h4>
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2011-09-13 17:44:24 +00:00
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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 operation was blocked by client/master synchronization.
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</p>
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</div>
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<div class="sect3" 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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3680610"></a>DB_SECONDARY_BAD</h4>
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2011-09-13 17:44:24 +00:00
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</div>
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</div>
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</div>
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<p>
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A secondary index references a nonexistent primary key.
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</p>
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</div>
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<div class="sect3" 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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2011-12-20 00:07:10 +00:00
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<h4 class="title"><a id="id3680804"></a>EINVAL</h4>
|
2011-09-13 17:44:24 +00:00
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</div>
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</div>
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</div>
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<p>
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If cursor methods other than <a class="xref" href="dbcget.html" title="DBcursor->get()">DBcursor->get()</a>
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or <a class="xref" href="dbcclose.html" title="DBcursor->close()">DBcursor->close()</a> were called;
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or if an invalid flag value or parameter was specified.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
|
2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3680885"></a>Class</h3>
|
2011-09-13 17:44:24 +00:00
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</div>
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</div>
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</div>
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<p>
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<a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a>
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</p>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
|
2011-12-20 00:07:10 +00:00
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<h3 class="title"><a id="id3680806"></a>See Also</h3>
|
2011-09-13 17:44:24 +00:00
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</div>
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</div>
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</div>
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<p>
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<a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a>
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|
</p>
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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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<td width="40%" align="left"><a accesskey="p" href="dbget_type.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="db.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="dbkey_range.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">DB->get_type() </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"> DB->key_range()</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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