Window functions do not let you do anything that was impossible to do with earlier
functionality, and they have nothing to do with the Microsoft Windows API. Using
previously available methods, such as self-joins, correlated subqueries, and cursors,
you can solve just about any T-SQL problem if you work at it long and hard enough. The
main benefit of window functions is the ease in which you can solve these tricky queries.
Most of the time, you also realize a big boost in performance over the older methods.
You can often use a window function to change a solution involving many statements or
subqueries to one easier statement.
