Hi Praveen,
You need to have Document number and Delivery status characteristics in your cube.
If the same is not available in 0pur_c01 you might need to create a new cube copying this cube and including the above 2 fields.
In Query Designer you have to create a new CKF for order count referencing characteristics document number and using exception aggregation to achieve the count.
Use to get the document count http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/009819ab-c96e-2910-bbb2-c85f7bdec04a?overridelayout=true
After that you have to create an RKF which would include the above created CKF for order count and also characteristics "Delivery status". This RKF would give you Open Order count based upon the condition of Delivery status which is empty when PO is open as suggested above by Anshul.
Hope you have got an idea.
Thanks
