title: SQL Count function won't work on joined query
body: <p>Got two tables.</p>
  
  <p>Artist:ArtistID,ArtistFirstName,ArtistLastName,ArtistEmail,ArtistPhone,Biography,ReferenceNumber,AgentID</p>
  
  <p>Agent:AgentID,AgentFirstName,AgentLastName,CompanyName,AgentEmail,AgentPhone</p>
  
  <p>Trying to list the number of artists represented by each booking agent</p>
  
  <p>note: an agent can represent many artists but each artist got one agent only. </p>
  
  <p>This is what I got and not sure why it is not working, Thanks</p>
  
  <pre><code>SELECT ag.AgentFirstName,ag.AgentLastName,ag.CompanyName,ag.AgentID,COUNT 
  (ar.ArtistID) AS NumberOfArtists
  FROM Agent ag
  JOIN Artist ar ON ar.AgentID  = ag.AgentID
  GROUP BY ArtistID
  </code></pre>