If I have understood your problem, what you want is to add data to date table. Join will not work, because you need at least a field to relate both tables apart from the date.
I think it would work something like:
purorder.date AS %date
order.date AS %date
stocks.date AS %date
prognosis.date AS %date
I'm not sure I understood the question either, but if so, see the attached example. It's not exactly your situation, but it connects three dates from three tables to the same master calendar. Two of the tables use the same ID, while the third uses a different ID. I guess ignore the third table, and you have something very like your situation.