Oracle 12c allows either a common user or local user to be created. Common user is created in container database. Common user name starts with c## and local user is created in plugged database
To find container database name
SQL> sho con_name
CON_NAME
------------------------------
CDB$ROOT
To find plugged databases
SQL> select name,open_mode from v$pdbs;
NAME OPEN_MODE
------------------------------ ----------
PDB$SEED READ ONLY
PDBORCL MOUNTED
To create a common user in CDB$ROOT
SQL> create user c##dummyuser identified by dummypwd;
To create a local user in PDB first set a dummy container
SQL> alter session set container=TEST;
Session altered.
SQL> create user test identified by test;
You cannot create a common user while in test session so if you try following you will get error
SQL> create user c##dummyuser identified by test;
create user c##dummyuser identified by test
*
ERROR at line 1:
ORA-65094: invalid local user or role name
Note:-
The reason for the error is that Local user name cannot be started with C##.
To find container database name
SQL> sho con_name
CON_NAME
------------------------------
CDB$ROOT
To find plugged databases
SQL> select name,open_mode from v$pdbs;
NAME OPEN_MODE
------------------------------ ----------
PDB$SEED READ ONLY
PDBORCL MOUNTED
To create a common user in CDB$ROOT
SQL> create user c##dummyuser identified by dummypwd;
To create a local user in PDB first set a dummy container
SQL> alter session set container=TEST;
Session altered.
SQL> create user test identified by test;
You cannot create a common user while in test session so if you try following you will get error
SQL> create user c##dummyuser identified by test;
create user c##dummyuser identified by test
*
ERROR at line 1:
ORA-65094: invalid local user or role name
Note:-
The reason for the error is that Local user name cannot be started with C##.