SQL Select Statement For Calculating A Running Average Column

Question

I am trying to have a running average column in the SELECT statement based on a column from the n previous rows in the same SELECT statement. The average I need is based on

Answer 1

Alternatively you can denormalize and store precalculated running values. Described here:

http://sqlblog.com/blogs/alexander_kuznetsov/archive/2009/01/23/denormalizing-to-enforce-business-rules-running-totals.aspx

Performance of selects is as fast as it goes. Of course, modifications are slower.