The idea is the you have many items in a container but you do not always have an item start date or container start date.
My goal is to get the average price of a vendorpart in a month of the year.
So now I group all ITEMS by VendorPartNumber, ITEMStartYear, ITEMStartMonth. Averaging the PRICE of this group... BUT Now the hard part is that if the ITEMStartYEAR or ITEMStartMonth is null then we must group the item via the Containers Month. BUT in the case where we are missing a date on the Item and its container, we will omit this set from the query.
In concept it seems simple... but I can not see how this translates into a query.