[twilight]

You can update summary when you modify records in the maintenance task table (add code to update and insert methods).
And / or you can create periodic operation for updating summary and schedule it to run at the batch server.
It is better to use separate table for storing summary values. Because, if you store in Employee table and user will modify it and in the same time be event for modifying summry values it will be a conflict - user will not be able to save data.