Why do I need a common account in Oracle? - oracle

Question

Why do I need a common account in Oracle 12c? A common means a CDB account. When I create an account using enterprise manager express it's creating only common accounts. Could I create a non-common account there? A common user also appears in every container I ever switch/connect to. What's the purpose of this common account to access all those pluggable databases?

Answer 1

Why do I need a common account in Oracle 12c?
What's the purpose of this common account to access all those pluggable databases?
You need a common account(common user) to perform administrative operations on CDB(container database) such as changing the state of a pluggable database, plugging and unplugging pluggable databases (PDBs) and so forth, which local user cannot do. Well, in fact, a local user can change state of pluggable database as well, but only PDB it connected to as sysdba or sysoper.
Could I create a non-common account there(in CDB)?
No, non-common account(Local user) cannot be created in the root - can only be created and operate within a pluggable database(PDB) and wont have access(you cannot use it to log in to) CDB or other PDBs.
Find out more
about commonality and common and local users.
Edit
CDB$ROOT is root container. PDB$SEED is just a template needed to create a pluggable databases. You cannot create or modify objects in it. PDBORCL is a pluggable database, which you should use for your development.
Oracle will throw the ORA-01033 error if you are trying to connect to a closed PDB as non sysdba user. Usually, PDBs database are not open by default, just mounted (unless your have automated that process by creating a trigger, for example, that will do it for you upon starting up CDB) and you need to explicitly open it while connecting as a common user (SYS or other common user that has the privilege to startup/alter pluggable database) and issue:
SQL> alter pluggable database <<name_of_PDB>> open;
or
SQL> startup pluggable database <<name_of_PDB>>
After that you should be able to connect to your PDB as common or local user. Of course they have to have appropriate privileges(create session) to be able to do so.
Edit #2 Automating starting up of pluggable database(s) on startup of CDB using system event(after startup on database) trigger. Unfortunately there is no native way to startup PDs automatically.
SQL> conn / as sysdba
Connected.
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> show pdbs
CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED READ ONLY NO
3 NKRASNOV READ WRITE NO
This specific trigger opens one pluggable database. If you have more than one PDs and want to open them all, the alter statement can be modified as follows ALTER PLUGGABLE DATABASE ALL OPEN;
SQL> create or replace trigger open_pdb
2 after startup on database
3 begin
4 execute immediate 'alter pluggable database nkrasnov open';
5 end;
6 /
Trigger created.
SQL> shutdown
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Database mounted.
Database opened.
SQL> show pdbs
CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED READ ONLY NO
3 NKRASNOV READ WRITE NO
SQL> conn hr/hr#nkrasnov_pdb
Connected.
SQL> spool off;