title: edit:SQL multiple table instances
body: <p>I have this table:</p>
  
  <pre><code>SUBSCRIPTION
  
  NAME SUBSCRIBER
  </code></pre>
  
  <p>It's essentially a table having a list of people who subscribe to each other. I want to write a query that outputs a list of tuples such that, if the set B represents all those people who subscribe to A, B also represents those people that A doesn't subscribe to. ie, find a list of people who are not mutually subscribed to each other.</p>
  
  <p>This is the query that I wrote:</p>
  
  <pre><code>SELECT A.name, B.name 
  FROM subscription AS A, subscription AS B 
  WHERE A.subscriber=B.name AND A.name!=B.subscriber;
  </code></pre>
  
  <p>ie, it should display two columns A and B where B subscribes to A and A doesn't subscribe to B.</p>
  
  <p>All I'm getting is garbage with a lot of rows duplicated. What am I doing wrong in this?</p>
  
  <p>Well, I made a mistake while stating the samples. The samples go like this:</p>
  
  <p>Melissa, Joan subscribe to John.
  Charles, John subscribe to Joan.
  Charles subscribes to Melissa.
  melissa, joan subscribe to Charles.</p>
  
  <p>the first part refers to the subscriber column and the second to the name column.
  ie, John's the name and melissa, joan subscribe to john.</p>
  
  <p>therfore, it should output (melissa,john) because john doesn't subscribe to melissa.</p>
  
  <p>How would this change the query?</p>