Quick check to verify weather I am on a multitenant db or non multitenant db

On a multitenant DB you can query v$database cdb column to find out weather your really on a multitenant DB or not. This should show 'YES'.

SQL> SELECT CDB FROM V$DATABASE;

CDB
---
YES

This is irrespective weather your connected to a cdb or pdb, should show you the result.
On the other hand if you connect to a non-multitenant database you will see the result as 'NO'.

SQL> SELECT CDB FROM V$DATABASE;

CDB
---
NO

This is as per oracle documentation. Tested to be correct on 12.1.0.1 version.
Thanks for paying a visit to this quick check link.