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DISTINCT per una sola colonna

Se stai utilizzando SQL Server 2005 o versioni successive, utilizza questo:

SELECT *
  FROM (
                SELECT  ID, 
                        Email, 
                        ProductName, 
                        ProductModel,
                        ROW_NUMBER() OVER(PARTITION BY Email ORDER BY ID DESC) rn
                    FROM Products
              ) a
WHERE rn = 1

EDIT:esempio utilizzando una clausola where:

SELECT *
  FROM (
                SELECT  ID, 
                        Email, 
                        ProductName, 
                        ProductModel,
                        ROW_NUMBER() OVER(PARTITION BY Email ORDER BY ID DESC) rn
                    FROM Products
                   WHERE ProductModel = 2
                     AND ProductName LIKE 'CYBER%'

              ) a
WHERE rn = 1