title: MySql - Select 3 tables and exclude if
body: <p>I got 3 tables a, b and c. Table a and b will be standalone, while table c will receive the id from both table a and b.</p>
  
  <p>What I would like is a query that would select the id from both table a and b. But it wouldn't select them <strong>IF</strong> they already(both) exist in table c.</p>
  
  <p>Note: There would be multiple entries in all tables</p>
  
  <p>Edit:</p>
  
  <p>Table a and b will have one column, whilst table c will have too(thought it was implied, my bad).
  A will have id, b will have id. But table c will have a_id and b_id</p>
  
  <p>example tables: <a href="http://sqlfiddle.com/#!9/714a6/11" rel="nofollow">http://sqlfiddle.com/#!9/714a6/11</a></p>