Queries :: Save Weekly Changes To A Table

We import data to a table on a weekly basis. We delete the table and replace the data. Most of the data is the same. It's date's, group names, ...

Now we would like to save the weekly table and add a saved date. Then we would like a query that puts all the saved tables together and that we could filter.

For example. A team is planned to do a work on 01/01/13. The next week it has changed to 07/01/13. So the data in the table it updated but we can't track the changed date. If we had the different tables we could filter that team and so that the work was originaly planned on date x to be done on the 01/01/13, on date y it was 07/01/13....

Of course if we would save the complete table every time it would mean a lot of useless data that hasn't changed. So a better solution would be that a query could see which data has changed and it only saved those lines on that date.