title: Sitecore Solr - IndexSchema no uniqueKey specified in schema
body: <p>I have a small extra question that I believe is related to
  <a href="https://stackoverflow.com/questions/31970849/missing-id-field-in-solr-index">Missing Id field in Solr index</a>  a little bit.</p>
  
  <p>The issue is that search result contain duplication items (that was edited), amount of item depends on edit count. 
  It is seems like sitecore doesn't remove old item from Solr index (no item versions).<br>
  Is it Sitecore issue or some specific Solr behavior ?</p>
  
  <p>I see in Solr log next message may be it is connected: </p>
  
  <blockquote>
    <p>WARN null IndexSchema no uniqueKey specified in schema.</p>
  </blockquote>