Index: kernel/db/dblist.php
===================================================================
--- kernel/db/dblist.php	(revision 14184)
+++ kernel/db/dblist.php	(working copy)
@@ -542,6 +542,11 @@
 		$order = $this->GetOrderClause();
 		$group = $this->GetGroupClause();
 
+		if ($for_counting) {
+			$optimizer = new LeftJoinOptimizer($q, $where . '|' . $having . '|' . $order . '|' . $group);
+			$q = $optimizer->simplify();
+		}
+
 		if (!empty($where)) $q .= ' WHERE ' . $where;
 		if (!empty($group)) $q .= ' GROUP BY ' . $group;
 		if (!empty($having)) $q .= ' HAVING ' . $having;
@@ -1105,4 +1110,172 @@
 		return true;
 	}
 
+}
+
+class LeftJoinOptimizer {
+
+	/**
+	 * Input sql for optimization
+	 *
+	 * @var string
+	 */
+	var $sql = '';
+
+	/**
+	 * All sql parts, where LEFT JOINed table aliases could be used
+	 *
+	 * @var string
+	 */
+	var $usageString = '';
+
+	/**
+	 * List of discovered LEFT JOINs
+	 *
+	 * @var Array
+	 */
+	var $joins = Array ();
+
+	/**
+	 * LEFT JOIN relations
+	 *
+	 * @var Array
+	 */
+	var $joinRelations = Array ();
+
+	/**
+	 * LEFT JOIN table aliases scheduled for removal
+	 *
+	 * @var Array
+	 */
+	var $aliasesToRemove = Array ();
+
+	function LeftJoinOptimizer($sql, $usage_string)
+	{
+		$this->sql = $sql;
+		$this->usageString = $usage_string;
+
+		$this->parseJoins();
+	}
+
+	/**
+	 * Tries to remove unused LEFT JOINs
+	 *
+	 * @return string
+	 */
+	function simplify()
+	{
+		if ( !$this->joins ) {
+			// no LEFT JOIN used, return unchanged sql
+			return $this->sql;
+		}
+
+		$this->updateRelations();
+		$this->removeAliases();
+
+		return $this->sql;
+	}
+
+	/**
+	 * Discovers LEFT JOINs based on given sql
+	 *
+	 */
+	function parseJoins()
+	{
+		if ( !preg_match_all('/LEFT\s+JOIN\s+(.*?|.*?\s+AS\s+.*?|.*?\s+.*?)\s+ON\s+(.*?\n|.*?$)/i', $this->sql, $regs) ) {
+			$this->joins = Array ();
+		}
+
+		// get all LEFT JOIN clause info from sql (without filters)
+		foreach ($regs[1] as $index => $match) {
+			$match_parts = preg_split('/\s+AS\s+|\s+/i', $match, 2);
+			$table_alias = count($match_parts) == 1 ? $match : $match_parts[1];
+
+			$this->joins[$table_alias] = Array (
+				'table' => $match_parts[0],
+				'join_clause' => $regs[0][$index],
+			);
+		}
+	}
+
+	/**
+	 * Detects relations between LEFT JOINs
+	 *
+	 */
+	function updateRelations()
+	{
+		foreach ($this->joins as $table_alias => $left_join_info) {
+			$escaped_alias = preg_quote($table_alias, '/');
+
+			foreach ($this->joins as $sub_table_alias => $sub_left_join_info) {
+				if ($table_alias == $sub_table_alias) {
+					continue;
+				}
+
+				if ( $this->matchAlias($escaped_alias, $sub_left_join_info['join_clause']) ) {
+					$this->joinRelations[] = $sub_table_alias . ':' . $table_alias;
+				}
+			}
+		}
+	}
+
+	/**
+	 * Removes scheduled LEFT JOINs, but only if they are not protected
+	 *
+	 */
+	function removeAliases()
+	{
+		$this->prepareAliasesRemoval();
+
+		foreach ($this->aliasesToRemove as $to_remove_alias) {
+			if ( !$this->aliasProtected($to_remove_alias) ) {
+				$this->sql = str_replace($this->joins[$to_remove_alias]['join_clause'], '', $this->sql);
+			}
+		}
+	}
+
+	/**
+	 * Schedules unused LEFT JOINs to for removal
+	 *
+	 */
+	function prepareAliasesRemoval()
+	{
+		foreach ($this->joins as $table_alias => $left_join_info) {
+			$escaped_alias = preg_quote($table_alias, '/');
+
+			if ( !$this->matchAlias($escaped_alias, $this->usageString) ) {
+				$this->aliasesToRemove[] = $table_alias;
+			}
+		}
+	}
+
+	/**
+	 * Checks if someone wants to remove LEFT JOIN, but it's used by some other LEFT JOIN, that stays
+	 *
+	 * @param string $table_alias
+	 * @return bool
+	 */
+	function aliasProtected($table_alias)
+	{
+		foreach ($this->joinRelations as $relation) {
+			list ($main_alias, $used_alias) = explode(':', $relation);
+
+			if ( ($used_alias == $table_alias) && !in_array($main_alias, $this->aliasesToRemove) ) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	/**
+	 * Matches given escaped alias to a string
+	 *
+	 * @param string $escaped_alias
+	 * @param string $string
+	 * @return bool
+	 */
+	function matchAlias($escaped_alias, $string)
+	{
+		return preg_match('/(`' . $escaped_alias . '`|' . $escaped_alias . ')\./', $string);
+	}
 }
\ No newline at end of file
Index: units/categories/categories_event_handler.php
===================================================================
--- units/categories/categories_event_handler.php	(revision 14184)
+++ units/categories/categories_event_handler.php	(working copy)
@@ -304,16 +304,16 @@
 					}
 				}
 				else {
-					$object->addFilter('parent_filter', 'ParentId = '.$parent_cat_id);
+					$object->addFilter('parent_filter', '%1$s.ParentId = '.$parent_cat_id);
 				}
 			}
 
-			$object->addFilter('perm_filter', 'PermId = 1'); // check for CATEGORY.VIEW permission
+			$object->addFilter('perm_filter', TABLE_PREFIX . 'PermCache.PermId = 1'); // check for CATEGORY.VIEW permission
 			if ($this->Application->RecallVar('user_id') != USER_ROOT) {
 				// apply permission filters to all users except "root"
 				$groups = explode(',',$this->Application->RecallVar('UserGroups'));
 				foreach ($groups as $group) {
-					$view_filters[] = 'FIND_IN_SET('.$group.', acl)';
+					$view_filters[] = 'FIND_IN_SET('.$group.', ' . TABLE_PREFIX . 'PermCache.ACL)';
 				}
 				$view_filter = implode(' OR ', $view_filters);
 				$object->addFilter('perm_filter2', $view_filter);
Index: units/modules/modules_event_handler.php
===================================================================
--- units/modules/modules_event_handler.php	(revision 14184)
+++ units/modules/modules_event_handler.php	(working copy)
@@ -37,7 +37,7 @@
 		{
 			$object =& $event->getObject();
 			if ($event->Special) {
-				$object->addFilter('current_module', 'Name = '.$event->Special);
+				$object->addFilter('current_module', '%1$s.Name = '.$event->Special);
 			}
 
 			$object->addFilter('not_core', '%1$s.Name <> "Core"');