Hey ...I'm new to SoapUI as well (less than a month) but I think you are looking in the wrong place to make a database connection. I believe, and I could be wrong, but if you are putting database connection info in the Authorization tab in the Request itself you indicating that the username password is for the application you are testing the Rest API for and NOT the database attached to the AUT (application under test). Right click on your test case name and select Add Step - then pick the JDBC Request choice and define the connection string info there - test it to make sure you made a connection and then supply your SQL statement in that step and see if that gets you what you want...
