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<! "@(#)compare.so 10.8 (Sleepycat) 10/29/98">
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<title>Berkeley DB Reference Guide: Access Methods</title>
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<h3>Berkeley DB Reference Guide: Access Methods</h3>
<p>
<h1 align=center>Sorting duplicate data items</h1>
<p>
Both the Btree and Hash access methods support duplicates, i.e., a
key item can have more than one data item associated with it. To
create a database that can support duplicates, you should specify
the <a href="../../api_c/DbInfo/info.html#DB_DUP">DB_DUP</a> flag in the DB_INFO structure.
<p>
It is also possible to maintain duplicate records in sorted order.
This will minimize the effort needed to search them and to perform
logical joins using them. To create a database where the duplicates
are sorted, you should specify the <a href="../../api_c/DbInfo/info.html#DB_DUPSORT">DB_DUPSORT</a> flag in the
DB_INFO structure.
<p>
The sort order for duplicates in the underlying database can also be
specified as part of the <a href="../../api_c/Db/open.html">db_open</a> call to open the database,
specifically by setting the dup_compare element of the
DB_INFO structure. If the <a href="../../api_c/DbInfo/info.html#DB_DUPSORT">DB_DUPSORT</a> flag is specified
and no comparison routine is specified, duplicates are maintained in a
default lexical order.
<p>
For information on how searching and insertion behaves in the
presence of duplicates (sorted or not), see the <a href="../../api_c/Db/get.html">DB->get</a>,
<a href="../../api_c/Db/put.html">DB->put</a>, <a href="../../api_c/Dbc/get.html">DBcursor->c_get</a> and <a href="../../api_c/Dbc/put.html">DBcursor->c_put</a> functions.
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