Inside Microsoft® SQL Server® 2008: T-SQL Querying

OVER Clause

The OVER clause allows you to request window-based calculations—that is, calculations performed over a whole window of rows. In Chapter 6, I described in detail how you use the OVER clause with analytical ranking functions. Microsoft SQL Server also supports the OVER clause with scalar aggregate functions; however, currently you can provide only the PARTITION BY clause. Future versions of SQL Server will most likely also support the other ANSI elements of aggregate window functions, including the ORDER BY and ROWS clauses.

The purpose of using the OVER clause with scalar aggregates is to calculate, for each row, an aggregate based on a window of values that extends beyond that row—and to do all this without using a GROUP BY clause in ...