title: Extract an array from a postgres json column and map it
body: <pre><code>create table test(a json);
  
  insert into test(a) 
  values('{"orders":[{"orderId":1}, {"orderId":2, "status":"done"}, {"orderId":3}]}');
  </code></pre>
  
  <p>Given the structure above, can I get an array or set of orderIds that are not 'done'?  And by that, I mean can I get the orderIds from with sql or plpgsql?  </p>
  
  <p>Any advice would be great!  Thank you very much!</p>