sql newbee needs help with query

Hi,

I'm new to sql and am working on a contact management program. One of the functionalities of this program is that the user can make queries based on user defined criteria (kind of like Lotus Approach). I need to incorporate the following into the criteria that users can select.

I have two database tables:

Contact
Donations

Contact contains our contacts (people).
Donations contains any donations those people may have given.


So, say Joe Blow (contact) has given 5 donations in the past year, $5, $50, $10, $100, $25 -- the total being $190.

Each donation is a separate record and the field that contains the amount for each donation is called "donation_amount".

Now, I need to be able to query with the total donation amount of one contact as one of the criteria.

For example:

The user of this program wants to know all the contacts who have given a total of at least $150 in the past year.

How do I do that? I know how to do everything except the total of donations. And not only do I have to be able to do it, it has to be dynamic somehow.

Can anyone help me with this?

If I need to explain more, let me know.

Thanks,
Daniel Lorimer