/** append a SQL string to the query field. Return the added SQL.
	* @param number $rowCount The maximum number of rows to retrieve
	* @param number $offset The index of the first row to retrieve
	*/
	function limit($rowCount, $offset=0) {
		$sql = " LIMIT ";
		$sql .= (int) $offset;
		$sql .= ", ";
		$sql .= (int) $rowCount;
		$this->query .= $sql;
		return $sql;
	}