Grant privileges on Roles but user cannot be granted - oracle

Question

I have grant Roles for users and grant some privs on Roles:
--Grant roles for users
GRANT DataEntry TO John, Joe, Lynn;
GRANT Supervisor TO Fred;
GRANT Management TO Amy, Beth;
--Grant on table to roles
GRANT SELECT, INSERT, UPDATE ON Attendance TO DataEntry;
GRANT SELECT, DELETE ON Attendance TO Supervisor;
GRANT SELECT ON Attendance TO Management;
However, when I query to dba_sys_privs table and select on John user, for example, I do not have privs which DataEntry role have? What happened with that problem?

Answer 1

John has been granted the role, not the privileges of the role directly. John will be able to take advantage of those privileges through the role. This means that if you were to revoke the role from the user, Oracle wouldn't need to go back and figure out which privileges were obtained through the role and revoke those too - this would be a challenge as a user might be granted multiple roles that provide the say privilege. It is much more efficient for Oracle to check if a user has access to a necessary privilege at parse time (which doesn't happen often).
If you want to see all the table privileges a user is able to use then you would need to look at both dba_tab_privs and dba_role_privs. Remember that a role can be granted another role so you would need to do a recursive query to identify all of those too:
with grantees (schema) as
(Select username schema
from dba_users
where username = 'JOHN'
union all
select rp.granted_role
from grantees g
join dba_role_privs rp
on g.schema = rp.grantee
)
select *
from dba_tab_privs sp
where sp.grantee in (select g.schema from grantees g)