title: Avoiding multiple streaming queries
body: <p>I have a structured streaming query which sinks to Kafka.  This query has a complex aggregation logic.</p>
  
  <p>I would like to sink the output DF of this query to multiple Kafka topics each partitioned on a different ‘key’ column.  I don't want to have multiple Kafka sinks for each of the different Kafka topics because that would mean running multiple streaming queries - one for each Kafka topic, especially since my aggregation logic is complex.</p>
  
  <p>Questions:</p>
  
  <ol>
  <li><p>Is there a way to output the results of a structured streaming query to multiple Kafka topics each with a different key column but without having to execute multiple streaming queries?</p></li>
  <li><p>If not,  would it be efficient to cascade the multiple queries such that the first query does the complex aggregation and writes output to Kafka and then the other queries just read the output of the first query and write their topics to Kafka thus avoiding doing the complex aggregation again?</p></li>
  </ol>
  
  <p>Thanks in advance for any help.</p>