Thanks for your post Blah Baby.

It seems that the Row_Number() clause is the cause of the slow running, rather than the CTE itself.

(Worrying given the subject of my article was the former, and not the latter. 🙁 )

For example, the following is fast:

;WITH BookCTE (BookTitle, BookEdition)

AS

(

select booktitle, max(bookedition) as bookedition from books group by booktitle

)

SELECT b.BookTitle, b.BookEdition, b.BookPublishDate, b.BookAuthor

FROM dbo.Books b INNER JOIN BookCTE c ON b.BookTitle=c.BookTitle AND b.BookEdition=c.BookEdition

The issue of why ROW_NUMBER() is signifcantly slower as data volumes increase in this case, is counter-intuitive to me, and needs additional research.

Thanks again.

Lawrence.