title: How to select the relative complement of a table B in a table A (A \ B) in an SQL-Query?
body: <p>I've got two tables:</p>
  
  <ol>
  <li><p>subjects:
  [id, ...]</p></li>
  <li><p>categories:
  [subject.id, ...]</p></li>
  </ol>
  
  <p>I want to select all subjects from table #1 without the entries in #2 (categories).</p>
  
  <p>Any tips appreciated (:</p>
  
  <p>best regards</p>