<!--$Id: db_key_range.html,v 1.2 2004/03/30 01:21:42 jtownsen Exp $--> <!--Copyright 1997-2003 by Sleepycat Software, Inc.--> <!--All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB: DB->key_range</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> </head> <body bgcolor=white> <a name="2"><!--meow--></a> <table width="100%"><tr valign=top> <td> <h3>DB->key_range</h3> </td> <td align=right> <a href="../api_c/api_index.html"><img src="../images/api.gif" alt="API"></a> <a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a> </td></tr></table> <hr size=1 noshade> <tt> <h3><pre> #include <db.h> <p> int DB->key_range(DB *db, DB_TXN *txnid, DBT *key, DB_KEY_RANGE *key_range, u_int32_t flags); </pre></h3> <hr size=1 noshade> <h3>Description: DB->key_range</h3> <p>The DB->key_range method returns an estimate of the proportion of keys that are less than, equal to, and greater than the specified key. The underlying database must be of type Btree.</p> <p>The DB->key_range method fills in a structure of type DB_KEY_RANGE. The following data fields are available from the DB_KEY_RANGE structure:</p> <p><dl compact> <dt>double less;<dd>A value between 0 and 1, the proportion of keys less than the specified key. <dt>double equal;<dd>A value between 0 and 1, the proportion of keys equal to the specified key. <dt>double greater;<dd>A value between 0 and 1, the proportion of keys greater than the specified key. </dl> <p>Values are in the range of 0 to 1; for example, if the field <b>less</b> is 0.05, 5% of the keys in the database are less than the <b>key</b> parameter. The value for <b>equal</b> will be zero if there is no matching key, and will be non-zero otherwise.</p> <p>The DB->key_range method returns a non-zero error value on failure and 0 on success. </p> <h3>Parameters</h3> <p><dl compact> <p><dt><b>key</b><dd> The key <a href="../api_c/dbt_class.html">DBT</a> operated on. <p><dt><b>key_range</b><dd> The estimates are returned in the <b>key_range</b> parameter, which contains three elements of type double: <b>less</b>, <b>equal</b>, and <b>greater</b>. Values are in the range of 0 to 1; for example, if the field <b>less</b> is 0.05, 5% of the keys in the database are less than the <b>key</b> parameter. The value for <b>equal</b> will be zero if there is no matching key, and will be non-zero otherwise. <p><dt><b>txnid</b><dd> If the operation is to be transaction-protected, the <b>txnid</b> parameter is a transaction handle returned from <a href="../api_c/txn_begin.html">DB_ENV->txn_begin</a>; otherwise, NULL. The DB->key_range method does not retain the locks it acquires for the life of the transaction, so estimates may not be repeatable. <p><dt><b>flags</b><dd> The <b>flags</b> parameter is currently unused, and must be set to 0. </dl> <h3>Errors</h3> <p>The DB->key_range method may fail and return one of the following non-zero errors:</p> <p><dl compact> <p><dt>DB_LOCK_DEADLOCK<dd>A transactional database environment operation was selected to resolve a deadlock. <p><dt>DB_LOCK_NOTGRANTED<dd>A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time. </dl> <p><dl compact> <p><dt>DB_REP_HANDLE_DEAD<dd>The database handle has been invalidated because a replication election unrolled a committed transaction. </dl> <p><dl compact> <p><dt>EINVAL<dd>If the underlying database was not of type Btree; or if an invalid flag value or parameter was specified. </dl> <hr size=1 noshade> <h3>Class</h3> <a href="../api_c/db_class.html">DB</a> <h3>See Also</h3> <a href="../api_c/db_list.html">Databases and Related Methods</a> </tt> <table width="100%"><tr><td><br></td><td align=right> <a href="../api_c/api_index.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a> </td></tr></table> <p><font size=1><a href="../sleepycat/legal.html">Copyright (c) 1996-2003</a> <a href="http://www.sleepycat.com">Sleepycat Software, Inc.</a> - All rights reserved.</font> </body> </html>