title: Select specific column value with sqlalchamey based on filter
body: <p>Been messing around with SQLalchemy and Flask and have run up into a problem that I can't find good documentation on. </p>
  
  <p>I need to query for the email of a specific user, but I can't figure the right combination of filter and select the specific column. </p>
  
  <p>I've tried:</p>
  
  <pre><code>user = User.query.filter(User.username == currentuser).email
  
  user = User.query(User.email).filter(User.username == currentuser)
  
  user = User.query.filter(User.username == currentuser, User.email)
  
  user = User.query.filter(User.email, User.username == currentuser)
  </code></pre>
  
  <p>But I'm not able to get the results I want.</p>