SQL Question - maybe lead and rank

Hi,

I have a problem, I have the following 2 rows:

Start Date End Date Item Used
10/05/04 10/06/04 A
10/05/04 10/10/04 B

As you can see the usage of items A and B overlap, both items A and B are used at the same time for a while, but the usage of A stops after a while and item B is used on it's own.

I need to be able to get them into the following rows:

Start Date End Date Item Used
10/05/04 10/06/04 A
10/05/04 10/06/04 B
11/06/04 10/10/04 B

So I need to know when B was used without A, and then know when B was used on it's own.

I thought of using lead or rank analytic functions, but I have no idea can anybody help?

Thanks

Daniel

i can give you a syntax if you like:
[code]select name, month, year, sum(salevalue),
rank() over (order by sum(saleValue) desc) as salesrank
from sale, salesrep, time
where sale.srid = salesrep.srid
and sale.code = time.code
group by name, month, year;