Managing Database Resources - OCP: Oracle Database 12c Administrator Certified Professional - page 495

The root and each PDB have their own data files. Individual PDBs can have their own
temporary tablespaces.
Chapter 12, “Managing Oracle Multitenant Databases,” describes container
databases (CDBs) and pluggable databases (PDBs) in detail. At this point,
you need to know that a CDB may contain zero or more PDBs, and a PDB
is collection of schemas, schema objects, and non-schema objects that
would appear to be an independent database. Also, a common user is a
database user who has the same identity in the root container and in every
PDB in a CDB.
Manage Permanent and Temporary Tablespaces
in CDB and PDBs
To manage tablespaces in a CDB you use the ALTER DATABASE statement, using the following
guidelines:
■ A permanent tablespace may be associated with only one container.
■ When a tablespace is created in a container it is associated with that container.
■ A CDB can have only one active UNDO tablespace.
■ Each instance of an Oracle RAC CDB can have only one active UNDO tablespace.
■ A CDB has one default temporary tablespace. The root and PDBs can use it.
■ A PDB can have its own temporary tablespaces.
Use the STORAGE clause in a CREATE PLUGGABLE DATABASE or ALTER PLUGGABLE DATABASE
statement to assign the data file size for a PDB.
Managing Permanent Tablespaces in the CDB and PDBs
A permanent tablespace may be associated with only one container: the root or a PDB.
Containers may not share default permanent tablespaces; each must have its own. A user
who does not have an assigned default tablespace will use the container's default tablespace.
Changing the Default Permanent Tablespace for the Root
To set the default tablespace for the root, connect to the target and enter the following
command, making sure the tablespace already exists in the root.
SQL> ALTER DATABASE DEFAULT TABLESPACE root_tablespace;
System altered.
Now a user whose current container is the root that is not explicitly assigned a
tablespace uses the root_tablespace as the default permanent tablespace.