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<!--$Id: db_key_range.so,v 10.23 2004/08/13 03:38:55 bostic Exp $-->
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<title>Berkeley DB: DB->key_range</title>
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<h3>DB->key_range</h3>
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<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>
<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>
<dl compact>
<dt><b>key</b><dd>The key <a href="../api_c/dbt_class.html">DBT</a> operated on.
<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.
<dt><b>txnid</b><dd>If the operation is part of an application-specified
transaction, 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. If no transaction
handle is specified, but the
operation occurs in a transactional
database,
the operation will be implicitly transaction protected. The DB->key_range method does not retain the locks it acquires for the
life of the transaction, so estimates may not be repeatable.
<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>
<dl compact>
<dt>DB_LOCK_DEADLOCK<dd>A transactional database environment operation was selected to resolve
a deadlock.
<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>
<dl compact>
<dt>DB_REP_HANDLE_DEAD<dd>The database handle has been invalidated because a replication election
unrolled a committed transaction.
<dt>DB_REP_LOCKOUT<dd>The operation was blocked by client/master synchronization.
</dl>
<dl compact>
<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>
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