如果把數據庫從11g 升級到12c，或者在12c中創建的，就是NON CDB，那麼這樣的數據庫就是普通的單實例，和12c 之前的數據庫沒有區別，但12c 的特點就是CDB 管理，所以既然上12c，還是要切換成CDB 進行管理。
所以下面的測試步驟，就是把NON CDB 切換成CDB的步驟。Oracle 12c Non CDB 數據庫 切換成 CDB 測試
[oracle@ogg6 preupgrade]$ sqlplus / as sysdba
SQL*Plus: Release 12.1.0.2.0 Production on Fri Sep 21 09:23:22 2018
Copyright (c) 1982, 2014, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
SQL> select name,cdb from v$database;
NAME CDB
--------- ---
OGG6 NO
SQL> select * from v$version;
BANNER CON_ID
-------------------------------------------------------------------------------- ----------
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production 0
PL/SQL Release 12.1.0.2.0 - Production 0
CORE 12.1.0.2.0 Production 0
TNS for Linux: Version 12.1.0.2.0 - Production 0
NLSRTL Version 12.1.0.2.0 - Production 0