Index: modules/user/user.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.module,v
retrieving revision 1.893
diff -u -p -r1.893 user.module
--- modules/user/user.module	6 Feb 2008 19:38:28 -0000	1.893
+++ modules/user/user.module	7 Feb 2008 13:08:11 -0000
@@ -759,7 +759,7 @@ function user_block($op = 'list', $delta
           // Perform database queries to gather online user lists.  We use s.timestamp
           // rather than u.access because it is much faster.
           $anonymous_count = sess_count($interval);
-          $authenticated_users = db_query('SELECT DISTINCT u.uid, u.name, s.timestamp FROM {users} u INNER JOIN {sessions} s ON u.uid = s.uid WHERE s.timestamp >= %d AND s.uid > 0 ORDER BY s.timestamp DESC', $interval);
+          $authenticated_users = db_query('SELECT u.uid, u.name FROM {users} u WHERE u.uid IN (SELECT s.uid FROM {sessions} s WHERE s.timestamp > %d AND s.uid > 0 ORDER BY s.timestamp DESC)', $interval);
           $authenticated_count = 0;
           $max_users = variable_get('user_block_max_list_count', 10);
           $items = array();