Oracle Database queries

To know the current user in Oracle

select user from dual;

Steps to know list of users in the Oracle database.

Connec to dba user

conn sys/password as sysdba;

execute below query to get list of users

select * from dba_users;

To select only user names:

select username from dba_users;

To know the full details about the user:

select * from dba_users where username='scott';

To get the Table space name:

select tablespace_name from dba_tablespaces;

To list the username and size of the user:

select owner,sum(bytes) from dba_segments group by owner;