A quick post as a reminder for myself some time down the road. After all, we all need reminders every once in a while!
Prior to Oracle Database 12c finding a list of default users within the database was always a pain. In Oracle Database 12c or later, this has become much simpler. Oracle introduced a column on the *_users views that allows the end users to identify what users are maintained by Oracle. This column name is ORACLE_MAINTAINED. The value of the column is either “N” or “Y”. If it is “Y”, then user account is maintained by Oracle.
A simple query of the ALL_USERS view will return about 57 different accounts that are maintained by Oracle in Oracle Database 19c (Autonomous Data Warehouse).
select * from all_users where oracle_maintained = 'Y' order by username;
For more information, the Oracle Database 19c docs can be referenced here.