title: Join multiple rows into a single column
body: <p>I have to create a report based on 2 files, table1 is the master file, table2 is an Attributes file. Is possible to join these two files and create the below resultant table.</p>
  <p>Table1:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>ID</th>
  <th>NUM</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>A</td>
  <td>1</td>
  </tr>
  <tr>
  <td>B</td>
  <td>1</td>
  </tr>
  <tr>
  <td>B</td>
  <td>2</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>Table2:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>ID</th>
  <th>NUM</th>
  <th>ATTR</th>
  <th>VAL</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>A</td>
  <td>1</td>
  <td>ATR1</td>
  <td>BLUE</td>
  </tr>
  <tr>
  <td>A</td>
  <td>1</td>
  <td>ATR2</td>
  <td>GREEN</td>
  </tr>
  <tr>
  <td>A</td>
  <td>1</td>
  <td>ATR3</td>
  <td>RED</td>
  </tr>
  <tr>
  <td>B</td>
  <td>2</td>
  <td>ATR1</td>
  <td>WHITE</td>
  </tr>
  <tr>
  <td>B</td>
  <td>2</td>
  <td>ATR2</td>
  <td>PINK</td>
  </tr>
  <tr>
  <td>B</td>
  <td>2</td>
  <td>ATR3</td>
  <td>RED</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>Resultant table:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>ID</th>
  <th>NUM</th>
  <th>ATTR1</th>
  <th>ATTR2</th>
  <th>ATTR3</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>A</td>
  <td>1</td>
  <td>BLUE</td>
  <td>GREEN</td>
  <td>RED</td>
  </tr>
  <tr>
  <td>B</td>
  <td>2</td>
  <td>WHITE</td>
  <td>PINK</td>
  <td>RED</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>Thank you very much!</p>