Unable to drop a user

I want to drop a 开发者_JS百科user like 'salman'. I have tried this syntax:

drop user "'salman'"

but it is not dropping.

Secondly, I want to drop a single database by command not from dbca. Is it possible?

You may need the DROP USER system privilege. But if you have that, the syntax should be:

DROP USER salman;

If you want to drop the user and all of the objects he owns:

DROP USER salman CASCADE;