Execute the following Microsoft SQL Server Transact-SQL demonstration scripts in Management Studio Query Editor.

USE AdventureWorks;

GO

SELECT ContactID

FROM   Person.Contact

EXCEPT

SELECT ContactID

FROM   HumanResources.Employee;

GO

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-- UNIQUE records - Applying OVER PARTITION BY & EXCEPT

------------

WITH CTE  AS (SELECT SalesOrderID,

  RN=ROW_NUMBER() OVER(PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID)

  FROM AdventureWorks2008.Sales.SalesOrderDetail

  WHERE ProductID > 799)

SELECT  SalesOrderID  FROM CTE WHERE RN=1

EXCEPT

SELECT  SalesOrderID  FROM CTE WHERE RN>1

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Related articles:

Using UNION, EXCEPT and INTERSECT with Other Transact-SQL Statements

http://www.sqlusa.com/bestpractices2008/compare-tables/