Managing Oracle Multitenant Databases - OCP: Oracle Database 12c Administrator Certified Professional - page 554

The CONTAINER Clause
When you create a new user, the CONTAINER clause differentiates the local user from the
common user. If you want to create a common user, make sure your current container is
CDB$ROOT and use CONTAINER = ALL when issuing the CREATE USER statement. This is the
default if you're logged into CDB$ROOT .
If you want to create a local user in a PDB, set your current container to the PDB and
use the CONTAINER = CURRENT clause. This is the default if you're logged into a PDB.
When creating a common user the DEFAULT TABLESPACE , TEMPORARY TABLESPACE , QUOTA ,
and PROFILE specified must exist in all the containers belonging to the CDB.
The Current Container
The current container is where the current session is running, and each session can have only
one current container at any point in time. It can be the root for common users or a PDB for
local and common users. Each container has a separate data dictionary, so the current con-
tainer data dictionary is used for privilege authorization and name resolution.
Chapter 14, “Oracle Security in CDBs and PDBs,” goes into greater detail
about users, roles, and privileges in CDBs and PDBs.
Establishing Connections to a CDB
This section describes using SQL*Plus to access the root of a CDB. You can connect to a
CDB by starting SQL*Plus with a connect string to the CDB, using the SQL*Plus CONNECT
command if you're already logged on, or you can switch from a PDB to the CDB$ROOT by
using the ALTER SESSION SET CONTAINER = CDB$ROOT SQL statement.
Clients access the root through a database service that has the same name as the data-
base name. With the service name, you can access the CDB$ROOT using the easy connect
syntax or the net service name configured in the tnsnames.ora file. When you create a new
database using the DBCA, it creates a new listener service handler, and a service name is
created in the local tnsnames.ora file. Oracle Net Services must be configured for you to
connect to the CDB$ROOT using a net service name.
The SESSIONS initialization parameter limits the total number of sessions that may be
established in a CDB and its PDBs. If you reach the SESSIONS limit, you will not be able to
log on.
Connecting to a CDB Using SQL*Plus
In Exercise 12.1, we will establish connections to a CDB and its DBA-created PDBs. This
exercise assumes that you have created a CDB and PDBs on your local machine and that
the CDB has been started.