title: remove duplicates from sql union
body: <p>I'm doing some basic sql on a few tables I have, using a union(rightly or wrongly)</p>
  
  <p>but I need remove the duplicates. Any ideas?</p>
  
  <pre><code>select * from calls
  left join users a on calls.assigned_to= a.user_id
  where a.dept = 4 
  union
  select * from calls
  left join users r on calls.requestor_id= r.user_id
  where r.dept = 4
  </code></pre>