Postgresql : How to login as a NOSUPERUSER and create a database?
https://stackoverflow.com/questions/31819377/psql-login-fails-database-not-found?rq=1
I think I understood it. I should connect to an existing database to login as p5 user. Then I create another database "db5".
If postgresql could have allowed login and then allowed to create databases then it would have been an intuitive way.