title: Find the number of certifications held by people, grouped by planet.
body: <p>This is part of my SQL homework and I can't wrap my head around it.  It should have two colums, name and CertCount.  Where name = planet name.  and CertCount = total number of certificates all people with that homeworld have.  </p>
  
  <p>These are the tables i'm working with: <a href="http://pastebin.com/kNRNGQFv" rel="nofollow">http://pastebin.com/kNRNGQFv</a>  </p>
  
  <p>This is my query so far: </p>
  
  <pre><code>SELECT bsg_people.homeworld, (SUM(cid) 
   AS 'CertCount'
     FROM bsg_people 
     INNER JOIN bsg_cert_people ON id=cid)
  GROUP BY bsg_people.homeworld;
  </code></pre>
  
  <p>I just can't seem to figure this out because there is no value to count the number of certificates each person has.  I appreciate any help.</p>