title: Bigquery Rolling Count Distinct
body: <p>I'd like to have a rolling count for daily visitors</p>
  <p>Example.</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>date</th>
  <th>visitor</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>2022-02-01</td>
  <td>A</td>
  </tr>
  <tr>
  <td>2022-02-01</td>
  <td>B</td>
  </tr>
  <tr>
  <td>2022-02-01</td>
  <td>C</td>
  </tr>
  <tr>
  <td>2022-02-02</td>
  <td>D</td>
  </tr>
  <tr>
  <td>2022-02-02</td>
  <td>E</td>
  </tr>
  <tr>
  <td>2022-02-03</td>
  <td>C</td>
  </tr>
  <tr>
  <td>2022-02-03</td>
  <td>F</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I want the output to be:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>date</th>
  <th>count_visitor</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>2022-02-01</td>
  <td>3 <em>(ABC)</em></td>
  </tr>
  <tr>
  <td>2022-02-02</td>
  <td>5 <em>(DE)</em></td>
  </tr>
  <tr>
  <td>2022-02-03</td>
  <td>6 <em>(CF)</em></td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I can't seem to find the query for this. Kindly need your help/</p>