Jared Westover does the math:
Even though I enjoy using SQL Server, there are some things other tools do better. For example, calculating moving averages or rolling totals is often simpler in tools like Power BI or Excel. That’s because Microsoft built those programs with that functionality in mind. Recently, we had to optimize a complex moving average query written for SQL Server 2008R2. Surprise! There’s no built-in function for moving averages in SQL Server. But don’t worry; I’ll show you how to make it work.
Read on for the solution, as well as the mess we had to work with prior to SQL Server 2012.