To Check if database is Container Database in Oracle 12c

 [oracle@sourcetest ~]$ sqlplus '/ as sysdba'  
 SQL*Plus: Release 12.1.0.1.0 Production on Thu Jul 25 19:57:38 2013  
 Copyright (c) 1982, 2013, Oracle. All rights reserved.  
 Connected to:  
 Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production  
 With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options  
 SQL> select name,dbid,con_dbid,cdb,con_id from v$database;  
 NAME    DBID  CON_DBID CDB  CON_ID  
 --------- ---------- ---------- --- ----------  
 MYCDB   2166941381 2166941381 YES     0  
 The value of CDB yes tells us that its a container database, and its container ID is 0.