I have a situation where a queryhave a similar structure, where i need to display all the line items of the Order with the details of Price, qty and amount as well as calculated KF computed as (f Max Amount for an Order in all the lines of the order) .
any suggestions is appreciated
Create a CKF which is equal to Order amount. Depending on which BW version you are on, you can either enhance or edit the property of this CKF with exception aggregation set as MAX with reference char on 'line item'. Now create an RKF based on this CKF and restrict it on 'Line item' with restriction marked as 'constant selection'.
I haven't tried it, so it may or may not get you what you look for.