title: Database Join Logic for finding exception member
body: <p>I have 3 table </p>
  
  <pre><code>User (UserID)
  ROOM (RoomID, UserID)  ---the userID is the host
  RoomMember (RMid, RoomID, UserID)  ---the UserID is the people inside the room
  </code></pre>
  
  <p>This is an example of 1 user host a room .
  Then the Room member is those who inside the room.
  now, i want to invite more member that not within the room.
  how do I write a query to find those who not in the room AND also not a Host of the room.</p>
  
  <p>for SQL asp.net C#  query
  I not sure how to do this using inner Join .</p>