Be surprised...Perhaps you can educate me: does a SQL Server index "know" when a field value is NULL? And is the optimizer smart enough to winkle that out from inside a coalesce? If the answer to either is "no" then a full row scan is needed- obviously excluding the xml-derived join, which has nothing to do with the point.
BTW, what happened to your commongroundsolutions website?
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
