Although late to the party, why parse the table twice?
SELECT ProductID, ProductName,
CASE @OutputType WHEN 'CSV' THEN ProductDate END AS ProductDate
(Typed on phone, apologies if any code typing errors).
Excuse my typos and sometimes awful grammar. My fingers work faster than my brain does :-P
Please always remember to encapsulate your code in IFCode Markup. For example [code=sql] [/code]
to read Jeffs Guide on how to post SQL questions, and get swift and helpful answers from the community