title: Subtracting the results of two queries
body: <p>I have a DB with a query telling me how many keys total per specific room and another indicating how many per specific room are currently signed out. I'd like a create a third query indicating how many per room are now available.</p>
  
  <p>Access File: <a href="http://jumpshare.com/b/k7pEg4" rel="nofollow noreferrer">http://jumpshare.com/b/k7pEg4</a></p>
  
  <p>Query 1 (Keys per room)</p>
  
  <pre><code>SELECT r.room_name, count(r.room_id) AS Key_Count
  FROM keys AS k 
  INNER JOIN rooms AS r ON r.room_id = k.room_id
  GROUP BY r.room_id, r.room_name
  ORDER BY 2 DESC;
  </code></pre>
  
  <p>Query 2 (KPR Signedout)</p>
  
  <pre><code>SELECT r.room_name, Count(r.room_id) AS Key_Count
  FROM rooms AS r 
  INNER JOIN (keys AS k 
  INNER JOIN signin AS s ON k.key_id = s.key_id) ON r.room_id = k.room_id
  WHERE (((s.[return_date]) Is Null))
  GROUP BY r.room_name, r.room_id
  ORDER BY 2 DESC;
  </code></pre>
  
  <p>This is the result from query 1 and 2. If Room FY218 has 8 total keys and 2 keys currently signed out. Can I combine my queries to tell me this room has 6 keys remaining. If not how can I get this result.</p>
  
  <p><img src="https://i.stack.imgur.com/V4q2x.png" alt="enter image description here"></p>
  
  <p>These are my table and relationships:</p>
  
  <p><img src="https://i.stack.imgur.com/Gttee.png" alt="enter image description here"></p>