Microsoft® SQL Server 2012 Unleashed

SQL Server 2012 Enhancements to Windowing Functions

Basic windowing capabilities were first provided in SQL Server 2005 with the introduction of the OVER clause and four new ranking functions ROW_NUMBER, RANK, DENSE_RANK, and NTILE. By default, the OVER clause produces a single window over the entire result set, but use of the optional PARTITION BY clause lets you divide the result set up into distinct “windows,” one per partition. The ORDER BY option for the OVER clause provides the ability to generate cumulative calculations within each window.

In addition to the four ranking functions, SQL Server supported use of the traditional aggregate functions (SUM, COUNT, MIN, MAX, AVG) with the OVER clause along with the optional PARTITION BY clause. ...