title: Returning only rows with unique value in specific column (Postgres)
body: <p>Say I have the following query:</p>
  
  <pre><code>SELECT id, connected_tracks FROM track_nodes;
  </code></pre>
  
  <p>Which returns the following rows:</p>
  
  <pre><code>1 "1100 1100 1200"
  2 "1100 1100 1300"
  3 "1100 1100 1300"
  4 "1100 1200 1400"
  </code></pre>
  
  <p>How can I modify my query, so that I only return rows that are not duplicated ?</p>
  
  <p>Using the above example, I would only wish to return these rows:</p>
  
  <pre><code>1 "1100 1100 1200"
  4 "1100 1200 1400"
  </code></pre>
  
  <p>The important point is that I don't want ANY of the duplicated rows.</p>
  
  <p>I am using Postgres 9.3.</p>
  
  <p>Whenever I search for ways to do this, I find many, many references to using "DISTINCT". But as far as I can tell, this won't give the answer I want - I think it would also give me one row where the "connected_track" value is duplicated.</p>
  
  <p>Can anyone give me a pointer on how to do this ?</p>
  
  <p>Many thanks!</p>