title: Calculating % of COUNT with groupby function in bigquery
body: <p>Running into some issues figuring out how to add in an extra column that will give me the percentage of the total of the aggregate of the count function. The query I have looks like this:</p>
  <pre><code>
      Select
         count(*) AS num_rides,
         member_casual
      FROM `2020_bikeshare_data`
      GROUP BY member_casual
      ORDER BY num_rides DESC
  
  </code></pre>
  <p>And returns me this result:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>num_rides</th>
  <th>member_casual</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>2134988</td>
  <td>member</td>
  </tr>
  <tr>
  <td>1341217</td>
  <td>casual</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>And what I'd like to do is add a 3rd column that lists the percent of the total each membership makes up</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>num_rides</th>
  <th>member_casual</th>
  <th>perc_tot</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>2134988</td>
  <td>member</td>
  <td>61.4%</td>
  </tr>
  <tr>
  <td>1341217</td>
  <td>casual</td>
  <td>38.6</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>thoughts?</p>