title: How to unpivot multiple colums to rows in Bigquery sql
body: <p>I'm struggling to unpivot/pivot using SQL.</p>
  <p>I tried UNPIVOT function from BIGQUERY documentation but I succeded to unpivot only ONE colums by using the code below but not multiple at the same time</p>
  <pre><code>SELECT ... FROM
  UNPIVOT(mail_sent FOR metric IN (mail_sent))
  </code></pre>
  <p>Here is the table I've got</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>month</th>
  <th>mail_sent</th>
  <th>mail_received</th>
  <th>mail_opened</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>01</td>
  <td>2000</td>
  <td>1900</td>
  <td>500</td>
  </tr>
  <tr>
  <td>02</td>
  <td>2200</td>
  <td>2000</td>
  <td>700</td>
  </tr>
  <tr>
  <td>03</td>
  <td>1900</td>
  <td>1800</td>
  <td>400</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>Here is what I want to have, keep the <strong>month</strong> in colums and have ALL the rest in rows :</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>values</th>
  <th>01</th>
  <th>02</th>
  <th>03</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>mail_sent</td>
  <td>2000</td>
  <td>2200</td>
  <td>1900</td>
  </tr>
  <tr>
  <td>mail_received</td>
  <td>1900</td>
  <td>2000</td>
  <td>1800</td>
  </tr>
  <tr>
  <td>mail_opened</td>
  <td>500</td>
  <td>700</td>
  <td>400</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>Any idea of how to do it ? Thanks a lot !</p>