Best way to prevent multiple notifications for an event

I am setting up a notification system using the SQL Event Provider, and I have a question about preventing multiple notifications for a single event. The events are provided from a SQL select, and the notification emails are sent once a day. How does NS decide if it's already handled an event? If I change the email frequency, do I need to add a check in my SQL select, or does NS handle this?

Thanks
Erick

Chronicles tables can be used to prevent duplicate notifications. Check out ms-help://MS.SQLCC.v9/MS.SQLSVR.v9.en/sqlntsv9/html/17e2debd-485f-4962-b974-6be6597983f9.htm for more information.

HTH...