Editing

I think you mean to ask "what is the difference between public relations and employee relations?" In essence, there is not a difference. Employee relations is a specialty, a niche within public relations.

Community Relations is part of Public Relations, specifically focused on how the organizations can build mutualism relations with the group of people (community) surrounding.

Editing

There are multiple types and forms of corporate relations. These include public affairs and relations, community relations and reinvestment, and intracompany relations (through management communications and human resources) for example.