title: Solr join and get field from both entity in single core
body: <p>I am using two entity 1) Title and 2) ApprovalForm in single core. Here i have to retrieve both entity fields.</p>
  
  <pre><code>select t.TitleNo,ap.PlanNumber 
    From  titles as t join approvalform as ap
    on t.TitleNo = ap.TitleNumber;
  </code></pre>
  
  <p>1) Entity:Title</p>
  
  <pre><code> &lt;entity name="Titles" pk="id" dataSource="TitlesDB" query="select 'Titles' as SolrSource, TitleNo as id, TitleNo,
               Authors from titles&gt;
       &lt;field column="SolrSource" name="SolrSource"/&gt;
       &lt;field column="TitleNo" name="TitleNo"/&gt;
        &lt;field column="Authors" name="Authors"/&gt;
          .....
  &lt;/entity&gt;
  </code></pre>
  
  <p>2) Entity: ApprovalForm</p>
  
  <pre><code>      &lt;entity name="ApprovalForm" pk="id" dataSource="TitlesDB" query="select 'approvalform' as SolrSource, TitleNumber as id, 
               planNumber from titles&gt;
       &lt;field column="SolrSource" name="SolrSource"/&gt;
       &lt;field column="TitleNumber" name="TitleNumber"/&gt;
        &lt;field column="planNumber" name="planNumber"/&gt;
        ..............
  &lt;/entity&gt;
  </code></pre>
  
  <p>Join query  is :</p>
  
  <pre><code>     {!join from =TitleNo to = TitleNumber}
  </code></pre>
  
  <p>Here i want to select planNumber. ie., How can i select second entity table fields.</p>