useful reading here
http://sqlmag.com/sql-server-2012/how-use-microsoft-sql-server-2012s-window-functions-part-1
http://sqlmag.com/sql-server-2012/microsoft-sql-server-2012-how-write-t-sql-window-functions-part-2
http://sqlmag.com/sql-server-2012/sql-server-2012-how-write-t-sql-window-functions-part-3
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you can lead a user to data....but you cannot make them think
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