Averages

I have data in my table that is by date.

I've got Seven columns:

Day
Absolute Month
Brand
Campaign
Ad Group
Clicks
Impressions

The formula for calculating "click through rate" is "clicks / impressions". No problem to add in a formula column to do that by date. However, what I'm really wanting to do is this:

1. I want to provide ascending user filters - Day (or I'm okay even with Month), Brand, Campaign, Ad Group
2. I want the user to be able to see clicks by date range
3. I want the user to be able to see impressions by date range
4. I want the user to be able to see click through rate by date range.

In order to do this, the system needs to be continuously adding up a the numbers and performing the click through calculation by the user selected date range.

Is this possible? And can you help me?

What I don't want is an "average of an average".

Thanks,

Jamie