title: BigQuery GROUP_CONCAT and ORDER BY
body: <p>I am currently using BigQuery and GROUP_CONCAT which works perfectly fine. However, when I try to add a ORDER BY clause to the GROUP_CONCAT statement like I would do in SQL, I receive an error.</p>
  
  <p>So e.g., something like</p>
  
  <p><code>SELECT a, GROUP_CONCAT(b ORDER BY c)
  FROM test
  GROUP BY a
  </code></p>
  
  <p>The same happens if I try to specify the separator.</p>
  
  <p>Any ideas on how to approach this?</p>