Right - as I mentioned in my previous note, the problem is that stored procedures and multi-statement queries can both return multiple result sets. We can't easily use type inference to express the difference between "in this use of query, I want a single result" (the common case) and "in this other use of query, I expect three results, each with different shapes" (far less common), so we need something like a multiQuery function (and perhaps a MultiResult class) instead.

You can do it, but you have to use the Monoid class's functions, e.g.: "select " `mappend` "2 + 2"

For cases like your "show columns from" example, though, I prefer Chris's suggestion of creating a custom newtype with its own special Param instance.