Ok. Youre not talking about a jdbc test step here are you? This is java, right? So how are you running the command 'SELECT session_user, current_database();' in a groovyscript step? Event handler step? Startup/teardown steps?
If you post the relevant script we should be able to help out.
Im guessing your current_database() method is pointing at your postgresql db, so youd need to find where the parms are set and change them accordingly.
Depending on what version of ReadyAPI you have you should be able to see which database connections that have already been setup.
Gonna need more info i think to provide further help.