Solr从单核中的两个实体加入并获取字段

Question

我在单核中使用两个实体1）Title和2）ApprovalForm。在这里，我必须检索两个实体字段。

select t.TitleNo,ap.PlanNumber 
  From  titles as t join approvalform as ap
  on t.TitleNo = ap.TitleNumber;

1）实体：标题

 <entity name="Titles" pk="id" dataSource="TitlesDB" query="select 'Titles' as SolrSource, TitleNo as id, TitleNo,
             Authors from titles>
     <field column="SolrSource" name="SolrSource"/>
     <field column="TitleNo" name="TitleNo"/>
      <field column="Authors" name="Authors"/>
        .....
</entity>

2）实体：ApprovalForm

      <entity name="ApprovalForm" pk="id" dataSource="TitlesDB" query="select 'approvalform' as SolrSource, TitleNumber as id, 
             planNumber from titles>
     <field column="SolrSource" name="SolrSource"/>
     <field column="TitleNumber" name="TitleNumber"/>
      <field column="planNumber" name="planNumber"/>
      ..............
</entity>

加入查询是：

     {!join from =TitleNo to = TitleNumber}

这里我想选择planNumber。即。我如何选择第二个实体表字段。