title: Solr count distinct of specific field on group
body: <p>Using SOLR, I have indexed device specific events. Each event containins a MAC address (deviceID) and a date. I would like to compute the distinct number of devices per day. I have tried the following code based on the Stats component but it seems that the Distinct part does not work.</p>
  
  <pre><code>.../solr/collectionVRtft_shard1_replica1/
  query?q=":"
  facet=true&amp;
  facet.field=date
  &amp;facet.stat=stbCount:unique(deviceID)
  
  SQL equivalent code would be:
  SELECT date, count(DISTINCT deviceID)
  FROM...
  GROUP BY date;
  </code></pre>
  
  <p>Thank you!</p>