Nathan Niesen Well that is what I need you to ascertain. Show me the JDBC client code you would use to call STRING_IN and access the returned results. I have no problem adding support for database specific ways of handling things. I just think it is better left to users of that particular database to tell me those specifics rather than me investigating them.

As for your original comment... I can see that it may have been an oversight to not have ProcedureCallImpl delegate to CallableStatementSupport#registerParameters. But I also do not see how that is an issue here. If H2 does not support the OUT parameter, why would you register one? And if you are not registering one, why would the distinction matter? I have to make some guesses since you did not show your code; but I would assume your STRING_IN example would register just one parameter: the inValue.