Background
Running totals have long been the core of most financial systems, be statements or even balance calculations at a given point in time. Now it’s not the hardest thing to do in SQL Server but it is definitely not the fastest thing in the world either as each record has to be evaluated separately. Prior to SQL Server 2012, you have to manually define the window/subset in which you want to calculate you running total, normally we would define a row number with a window on a specific order or a customer depending on the requirements at hand.
Read more »