Had a play with this and was very impressed - nice job.

I played around and added this index

CREATE INDEX IX_#Purchase_ProductCode

ON #Purchase (

ProductCode)

INCLUDE (CustomerID)

One concern I had was looking at the query plan, the EXCEPT does a clustered index scan. That may be a function of the small data set, but I am not sure.

My preference for these types of queries has always been to do an OUTER JOIN on the one we don't want selected and then say that we only want the ones that didn't match returned.

SELECT a.CustomerID

FROM #Purchase a

LEFT OUTER JOIN #Purchase b

ON b.CustomerID = a.CustomerID

AND b.ProductCode IN ('C')

WHERE a.ProductCode IN ('A','B')

AND b.CustomerID IS NULL

GROUP BY a.CustomerID

HAVING COUNT(DISTINCT a.ProductCode) = 2

Any thoughts?