title: Using PostgreSQL Aggregate ORDER BY with sqlalchemy
body: <p>I have a query which uses PostgreSQL's syntax for using ORDER BY in an aggregate function, something like this:</p>
  
  <pre><code>SELECT some_agg_func(a ORDER BY b DESC) FROM table;
  </code></pre>
  
  <p>Does anyone know of anyway to do this with the sqlalchemy expression language?</p>