protected function _sql_left_join($skey, $sTable, $fkey, $fTable) {
		if (is_array($fTable))
			list($fTable,$fTable_alias) = $fTable;
		$skey = $this->db->quotekey($skey);
		$sTable = $this->db->quotekey($sTable);
		$fkey = $this->db->quotekey($fkey);
		$fTable = $this->db->quotekey($fTable);
		if (isset($fTable_alias)) {
			$fTable_alias = $this->db->quotekey($fTable_alias);
			return 'LEFT JOIN '.$fTable.' AS '.$fTable_alias.' ON '.$sTable.'.'.$skey.' = '.$fTable_alias.'.'.$fkey;
		} else
			return 'LEFT JOIN '.$fTable.' ON '.$sTable.'.'.$skey.' = '.$fTable.'.'.$fkey;
	}