Case statement for Cumulative sales

Cognos 8 Business Intelligence Report Studio
1

I need to show cumulative sales for certain product type.I wrote following expression it is giving error:

Running-total ([Order Item Details].[Order Item Details].[Net Sale Item Qty] for (case when [Order Item Details].[Application].[Platform Name] =‘ABC’ then
[Order Item Details].[Order Item Details].[Net Sale Item Qty]
else
null)
end
)

and if i need to show monthly,quaterly,yearly cumulative sales separately,how this case statement should be written
Appreciate your help

2

I wrote this expression for week up to yesterday

if (Order Item Details.Order Source.Order Source='GHJ’
and Order Item Details.Application.Platform Name='ABC’
and (Order Item Details.Activity Date.Short Date between _add_days (current_date,-7) and _add_days(current_date,-1)))
then
(running-total(Order Item Details.Order Item Details.Net Sale Amt (USD)))
else
(0)

But it is giving incorrect results.Thanks