When I give the command to drop a user i.e. DROP USER 'username' cascade,
Does it deletes all the tablespace and datafiles used by that particular user.
If not, what is the command to delete all the tablespace / datafiles / disk space that were used by that particular user.
After dropping the user, you need to, for each related tablespace, take it offline and drop it. For example if you had a user named 'SAMPLE' and two tablespaces called 'SAMPLE' and 'SAMPLE_INDEX', then you'd need to do the following:
You can check which table space is used by which user with the following query.
You can also see the list of table spaces by looking at the following tables