> It seems a bit odd that it's impossible to use merge with prepared statements > without specifically casting the source types (which I did now to continue my > experiment).
I have no comments on this. Maybe it can be improved, but I don't know how.
Not tested, but the example prepare command fails to make use of the optional data types specification. Using that should remove the need to cast the parameter placeholder within the query itself.
That said, in theory the INSERT specification of the MERGE could be used to either resolve unknowns or even forcibly convert the data types of the relation produced by the USING clause to match the actual types required for the INSERT (since that will happen at insert time anyway). This would make the UPDATE behavior slightly different than a top-level UPDATE command though, since that does not have the same context information.
