In principiu folositi tot o coloana calculata.

Formula pentru coloana depinde de logica aplicatiei care personal imi scapa.

Eventual puteti lua in calcul folosirea GROUP BY.

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Cristian Andrei Lefter, SQL Server MVP
MCT, MCSA, MCDBA, MCAD, MCSD .NET,
MCTS, MCITP - Database Administrator SQL Server 2005
http://sqlserver.ro