Calculate values based on two different date ranges

[enquirerfm]

I have a table which has certain $ values for the data. The data is collected at different dates. So for example:

12/3/2007 black t-shirt $4

1/1/2008 black t-shirt (they're not all black - let's say there are 50 different products) $3.9

2/4/2008 black t-shirt 4.1 etc etc etc

I want to find an average value for ea. qtr and then compare it to another qtr. So, I have written a script which creates a report for calculating values for any qtr. But I don't see how I can store this data and then use it to compare to another qtr - say, qtr 1 in 2007 to qtr 4 in 2010. The other complication is that some products may be deleted during this time, and others may come along. So even if I were to do this manually - I see I could do that - I can't easily match up the products.

Any ideas much appreciated. Thx.

[comment]

I am not sure I fully understand your question. I think you could find the records in both quarters and summarize them by quarter.

[Keith LaMarre]

I believe that you'll have to have a table for quarterly sales - that will be run and stored your data for the quarter (for each product) with at least this much data: Quarter - Year - ProductID - Number sold - Average Price...

You can then create some global relationships to compare a products quarterly sales to another quarter (or another product).

Of course, none of that data would be stored...(i.e. - the comparison will be looked at and then discarded.)