PHP echo不显示表标记

Question

我试图在表格中显示数据库的内容，我的表格作为标签出现。我有什么不对的吗？

这是我的代码：

 echo $content .= "<tr>
                <th>$route = $total_submit</th>
                </tr>";

    $content .= " <tr>

          <td>" .'DELIVRD'. "</td>
                <td>" . $total_deliv . "</td>
                </tr>";
     $content .= " <tr>
                <td>" .'UNDELIV'. "</td>
                <td>" . $total_undeliv . "</td>
                </tr>";
                $content .= " <tr>
                <td>" .'ACK'. "</td>
              <td>" . $total_ack . "</td>
                </tr>";
               $content .= " <tr>
               <td>" .'EXPIRED'. "</td>
                <td>" . $total_expired . "</td>
                </tr>";
             $content .= " <tr>
                <td>" .'REJECTD'. "</td>
                <td>" . $total_rejected . "</td>
                </tr>";
                 }
          $constt .= "<table border='1px'>
                 <tr>
                <th>ROUTE PERFORMANCE</th>
                </tr>";
 echo $constt .=$content."</table>" ;