How to obtain a cumulative value in a Query Table?

How to obtain a cumulative value in a Query Table?

I have the following query:

SELECT "D"."Date" as 'Date', ISNULL("O"."Opened",0) as 'Opened', ISNULL("C"."Closed",0) as 'Closed', (ISNULL("O"."Opened",0) - ISNULL("C"."Closed",0)) as 'Backlog Change'
FROM "Days" AS "D"
     LEFT JOIN "Opened by Day" as "O" on "D"."Date" = "O"."DATE"
     LEFT JOIN "Closed by Day" as "C" on "D"."Date" = "C"."DATE"

I want a 5th column called "Backlog" which is the cumulative sum of "Backlog Change".  I tried adding a query on a query table, nested sub-query, etc but cannot get anything to work.  Any ideas?