title: Returning values with same id as one row
body: <p>Apologies if this has been answered but trying to word this question was a nightmare to wrap my head around.</p>
  <p>Essentially I have a table</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th style="text-align: center;">post_id</th>
  <th style="text-align: center;">tag_id</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td style="text-align: center;">15618</td>
  <td style="text-align: center;">6</td>
  </tr>
  <tr>
  <td style="text-align: center;">15618</td>
  <td style="text-align: center;">109</td>
  </tr>
  <tr>
  <td style="text-align: center;">15618</td>
  <td style="text-align: center;">659</td>
  </tr>
  <tr>
  <td style="text-align: center;">27248</td>
  <td style="text-align: center;">245</td>
  </tr>
  <tr>
  <td style="text-align: center;">27248</td>
  <td style="text-align: center;">6</td>
  </tr>
  <tr>
  <td style="text-align: center;">27248</td>
  <td style="text-align: center;">7</td>
  </tr>
  <tr>
  <td style="text-align: center;">27248</td>
  <td style="text-align: center;">6499</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>and I essentially want a query that returns</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th style="text-align: center;">post_id</th>
  <th style="text-align: center;">tag_id</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td style="text-align: center;">15618</td>
  <td style="text-align: center;">6, 109, 659</td>
  </tr>
  <tr>
  <td style="text-align: center;">27248</td>
  <td style="text-align: center;">245, 6, 7, 6499</td>
  </tr>
  </tbody>
  </table>
  </div>