Database User Access information

To look up what role/access you have in an Oracle database we can use this query -

select * from dba_role_privs where grantee = 'userid';

Table structure of dba_role_privs:

Column Name    ID    Data Type
GRANTEE         1    VARCHAR2 (30 Byte)  
GRANTED_ROLE    2    VARCHAR2 (30 Byte) -- Roles defined specifically for the db
ADMIN_OPTION    3    VARCHAR2 (3 Byte)  
DEFAULT_ROLE    4    VARCHAR2 (3 Byte)  

If there's no entry for the user-id in this table that means user doesn't have access to the database.