Save and sort date and time in SQLite

I have a problem with this qoute:

SELECT _id, todo_name, todo_date_start, time_start FROM todo ORDER BY todo_date_start ASC

Is there an easy way to order my ToDos by the start-date (dd.mm.yyyy) and the start-time (hh:mm)? It still works with the order by days of the date.

The table is created with text-format:

COLUMN_DATE_START + " text not null, "
        + COLUMN_TIME_START + " text not null, "

Can anyone help me?