advanced microsoft access courses in london - Cumulative Total Query

Hi,

I am trying to produce a cumulative total in a query. I am using the DSum function and I can get this to work if I want to compare the ID number and add up totals in this order, but what I really need is to be able to compare dates and add up values in order of the date the action is expected to be completed:

I have three columns in this query - Value (the cost that I want to produce my cumulative total from), the cost ID (the primany key), and the expected cost date (the date the cost is due to come in)

I am hoping to use this query to produce a graph in a report to show how the costs spent over time.

This is the expresion i'm using:

Total Cost: DSum("[Value]","[CostsTable]","[Expected Cost Date] >=" & [InstallTable]![Circuit Expected Live Date])

If I exchange Expected Cost Date with the Cost ID then I can get this to add up, although not in the order I'm hoping to get. But when I use the Expected Cost Date I get blank cells.

Please can you let me know what I am doing wrong with this expresion?

Many thanks,
Caroline