Explanation/Reference:
Explanation:
* The CREATE DATABASE ... ENABLE PLUGGABLE DATABASE SQL statement creates a new CDB. If
you do not specify the ENABLE PLUGGABLE DATABASE clause, then the newly created database is a
non-CDB and can never contain PDBs.
Along with the root (CDB$ROOT), Oracle Database automatically creates a seed PDB (PDB$SEED). The
following graphic shows a newly created CDB:

* Creating a PDB
Rather than constructing the data dictionary tables that define an empty PDB from scratch, and then
populating its Obj$ and Dependency$ tables, the empty PDB is created when the CDB is created. (Here,
we use empty to mean containing no customer-created artifacts.) It is referred to as the seed PDB and has
the name PDB$Seed. Every CDB non-negotiably contains a seed PDB; it is non-negotiably always open in
read-only mode. This has no conceptual significance; rather, it is just an optimization device. The create
PDB operation is implemented as a special case of the clone PDB operation.

* SHUTDOWN [ABORT | IMMEDIATE | NORMAL | TRANSACTIONAL [LOCAL]]
Shuts down a currently running Oracle Database instance, optionally closing and dismounting a database. If the current database is a pluggable database, only the pluggable database is closed. The consolidated instance continues to run.
Shutdown commands that wait for current calls to complete or users to disconnect such as SHUTDOWN NORMAL and SHUTDOWN TRANSACTIONAL have a time limit that the SHUTDOWN command will wait. If all events blocking the shutdown have not occurred within the time limit, the shutdown command cancels with the following message:
ORA-01013: user requested cancel of current operation
* If logged into a CDB, shutdown closes the CDB instance.
To shutdown a CDB or non CDB, you must be connected to the CDB or non CDB instance that you want to close, and then enter SHUTDOWN
Database closed.
Database dismounted.
Oracle instance shut down.
To shutdown a PDB, you must log into the PDB to issue the SHUTDOWN command.
SHUTDOWN
Pluggable Database closed.
Note:
* Prerequisites for PDB Shutdown
When the current container is a pluggable database (PDB), the SHUTDOWN command can only be used if:
The current user has SYSDBA, SYSOPER, SYSBACKUP, or SYSDG system privilege.
The privilege is either commonly granted or locally granted in the PDB.
The current user exercises the privilege using AS SYSDBA, AS SYSOPER, AS SYSBACKUP, or AS SYSDG at connect time.
To close a PDB, the PDB must be open.

E: You can perform all ALTER PLUGGABLE DATABASE tasks by connecting to a PDB and running the corresponding
ALTER DATABASE statement. This functionality is provided to maintain backward compatibility for applications that
have been migrated to a CDB environment.
AG: When you issue an ALTER PLUGGABLE DATABASE OPEN statement, READ WRITE is the default unless a PDB being
opened belongs to a CDB that is used as a physical standby database, in which case READ ONLY is the default.
You can specify which PDBs to modify in the following ways:
List one or more PDBs.
Specify ALL to modify all of the PDBs.
Specify ALL EXCEPT to modify all of the PDBs, except for the PDBs listed.