@ Joe Celko:

You've demonstrated to design the view for YTD_Averages.

What is your recommendation to get MTD, QTD and ALL_avg?

As far as I can see, one option would be to UNION (ALL) 4 separate views using different WHERE clauses (resulting in 4 separate scan/seek operation) or to use the approach I posted that will use one table scan and several aggregated CASE statements.

It's nothing I would start arguing about but learning from.