Count distinct values of a field based on distinct count of another field
I have a FactOrderLine table where the Order_ID is repeated as many times as there are products ordered under the specific Order_ID. I want to count the distinct shipping dates based on the distinct count of Order_ID.
For example I have:
Order_ID, Shipping Date,ProductID
How can I set the expression in Qlik to have the distinct shipping date count based on the distinct count of the OrderID? For Each Order ID I need to pick the count of one date and the date can be the same for another Order_ID.
If I set a COUNT DISTINCT on Shipping Date this will not be correct I assume as I can have two same dates but belongings to a different Order_ID.