yup, briand is exactly correct. Just like with any real DB there are user 'roles' or permission levels. You will likely need to pass that along to the DB when you open the connection. Some users are 'read only' others are 'add only no modify', some are "sa" or 'sysadmin' level which are full access DB users and so on in various levels depending on how the DB designer setup the access security.

But it is usually all setup within the DB itself and not related to the system userid. Though some DB can work that way, it is doubtful your db was created that way because it's inherently insecure to someone determined to get into the db.