How to use SQL Developer with Oracle 12c

Thank you so much. I have gained a lot of knowledge from your videos.

Thank you for creating this video I loved it..

Awesome video, thanks for uploading..

I am getting ora-28000 the account is locked in SQL developer
Unable to unlock scott user in SQL plus :-

SQL> ALTER USER SCOTT ACCOUNT UNLOCK;
ALTER USER SCOTT ACCOUNT UNLOCK
*
ERROR at line 1:
ORA-01918: user 'SCOTT' does not exist

hello sir, when i m creating new database connection then its telling login denied and i type username n pwd that u mention in video...plz help me sir

Status : Failure -Test failed: Listener refused the connection with the following error:
ORA-12514, TNS:listener does not currently know of service requested in connect descriptor

Where is previous video