Just piping in on a something I just noticed in playing with INTERSECTand EXCEPT.  I expected that they would act identicle to EXISTS and NOT EXISTS but they don't.  They treat nulls differently.

Based on the author's example create a quick reference table.

SELECT

TOP 1000 CustomerID, OrderDate, SalesPersonID

INTO

Sales.SalesOrderHeaderIntersection

FROM

Sales.SalesOrderHeader

I expected the following two queries to return the same results.

SELECT

CustomerID, OrderDate, SalesPersonID FROM Sales.SalesOrderHeader INTERSECT

SELECT

CustomerID, OrderDate, SalesPersonID FROM Sales.SalesOrderHeaderIntersection

SELECT

CustomerID, OrderDate, SalesPersonID FROM Sales.SalesOrderHeader t1

WHERE

EXISTS

(

SELECT * FROM Sales.SalesOrderHeaderIntersection t2 WHERE t1.CustomerID=t2.CustomerID

AND t1.OrderDate=t2.OrderDate AND t1.SalesPersonID=t2.SalesPersonID)

They do not because [NOT] EXISTS ommitts the nulls as a non match while INTERSECT includes them