“Set Role” statement. ( Remember : It affects current session only )
Use the SET ROLE statement to enable and disable roles for your current session. This statement will be useful when you want to give special privilege to specific user for a specific period of time.
When a user logs on, Oracle Database enables all privileges granted explicitly to the user and all privileges in the user’s default roles. During the session, the user or an application can use the SET ROLE statement any number of times to change the roles currently enabled for the session.
You can see which roles are currently enabled by examining the SESSION_ROLES data dictionary view.