WebSocket listener for Microsoft SQL Database
Possible solution might be T-SQL triggers on INSERT or UPDATE with a CLR procedure which sends some notification to your main application, which then pumps data out to your client via websockets. Would avoid needing to poll the database.
Per your comment - not sure how AJAX would help you specifically in this case - because being a technology driven from the client (browser), your solution would again be polling, which I understand you want to avoid. WebSockets sounds like the right fit here because it gives you the ability to do true "push" from the server to the client without requiring a poll.
Obviously I'm talking in very general and theoretical terms here.