@robotdan Thank you @robotdan and @dan , I appreciate your time.
I have installed MySQL/J connector. Then I got an error saying :
The database and schema exist, but for some reason the ordinary user you specified cannot connect to it. Perhaps the user already existed and you provided the wrong password. The error from the database was [Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.]..
This is how Maintenance Mode Database Configuration looks :
I once provided a user credentials with superuser privileges but it still did not work and got the same error. Could you please give a clue ? Thank you...