title: What does @ do in Postgres function calls?
body: <p>I'm trying to figure out what a @ does in a Postgres function call. It is the worst term try to google or search for in the documentation. </p>
  
  <p>I can do:</p>
  
  <pre><code>SELECT @extract(epoch FROM valid_to - valid_from) FROM...
  </code></pre>
  
  <p>and</p>
  
  <pre><code>SELECT extract(epoch FROM valid_to - valid_from) FROM...
  </code></pre>
  
  <p>both seems to work. The version with @ I found in a example and I just don't find the purpose of it in any documentation or by googling.</p>
  
  <p>Anyone that knows what this is or can point out where to read more?</p>