SQL Server 2005 introduced only partial support for the OVER clause. It is our strong belief that a more complete implementation of the OVER clause should be prioritized highly in consideration for future enhancements in SQL Server.

A more complete implementation of the OVER clause can help in solving many common business problems with simpler, more intuitive, and faster solutions than available today and also substantially reduce the need for cursors.

The following paper details OVER clause feature enhancement requests:

"SQL Server Feature Enhancement Request – OVER Clause and Ordered Calculations by Itzik Ben-Gan and Sujata Mehta"

Direct link:
http://www.insidetsql.com/OVER_Clause_and_Ordered_Calculations.doc

Link from resources/whitepapers page:
http://www.insidetsql.com/resources.htm#Whitepapers

The document is long, detailing why those enhancements are needed and what is currently available in the product.

If you are already familiar with the problems related to ordered calculations, and with the existing support for the OVER clause in SQL Server 2005, feel free to jump directly to section 4, which details the OVER clause feature enhancement requests.

For those of you who believe that it is important to enhance the OVER clause, please cast your votes. I submitted multiple requests via the connect.microsoft.com website, each covering a separate feature enhancement request.
You can vote for the requests here:

https://connect.microsoft.com/SQLServer/feedback/SearchResults.aspx?SearchQuery=over+clause+enhancement

Or through the following individual links:

ORDER BY for aggregates:
https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=254387

LAG and LEAD functions:
https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=254388

TOP OVER:
https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=254390

Vector expressions for calculations based on OVER clause:
https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=254391

ROWS and RANGE window sub-clauses:
https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=254392

DISTINCT clause for aggregate functions:
https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=254393

FIRST_VALUE, LAST_VALUE functions:
https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=254395

Progressive ordered calculations:
https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=254397

Thanks for your support!
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BG