Apply filter but retain running total?

[dinos]

Hi,

I have a report that generates this output.

Period    Open    Credit    Close
1    0    200    200
2    200    0    200
3    200    200    400
4    400   100    500

I want to filter on Period 4, but retain the running total for Open, so that I would get this result.

Period    Open    Credit    Close
4    400    100    500

I applied a filter for period 4, but I lose everything before it, so i don't get the rolling total from the previous periods.  I know there is a simple solution to this...I can't figure it out.  Any ideas?

Cheers,

Diz

[ykud]

Just for further references:
You'll need two queries and either a join:
http://www-01.ibm.com/support/docview.wss?uid=swg21341261
or a filter on a second one.