title: count subscribers who have subscribed to all magazines(3 different magazines)
body: <pre><code>SUBSCRIPTIONS (SUB_ID, MAG_ID, RENEW_DATE, CANCEL_DATE, PERIOD)
  </code></pre>
  
  <p>This is what I tried but all i get is a count of 0</p>
  
  <pre><code>SELECT COUNT(DISTINCT SUB_ID)
  FROM DVD_SUBSCRIPTIONS
  WHERE MAG_ID = 1
  AND MAG_ID = 2
  AND MAG_ID = 3;
  
  
  COUNT(DISTINCTSUB_ID)
   ---------------------
                0
  </code></pre>
  
  <p>Help plzzz</p>