Calculating gaps between memberships (1 Viewer)

Hi

I am hoping someone can help me with a calculation I am finding incredibly tricky.

I am looking at peoples memberships, so have data structured like this:

Person ID Membership ID Membership Start Date Membership End Date
112233 98765 01/01/11 31/01/11
112233 12345 01/03/11 31/05/11
112233 67890 01/05/11 31/05/11

So, people can have had more than one membership.

What I am trying to find is the difference between the start date and end date of the memberships, and see if any were overlapping. So in the example above I would like to start at the first membership and compare this to the second, so the answer is 1 month difference between end date and next start date, then compare the second to the third, so the answer is -1 month between end date and start date.

I am completely stuck as to how I can do this.

Does anyone have any ideas? Any help would be greatly appreciated.

Thanks
Jobie

You can use this to get the relevant values on the same record, from which it should be a simple calculation:

http://allenbrowne.com/subquery-01.html#AnotherRecord