title: Filtering by using a varchar column in sql
body: <p>I have a table which has a date but stored as a <code>varchar</code> datatype column:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>my_date</th>
  <th>metric_name</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>2021-09-12</td>
  <td>CLS</td>
  </tr>
  <tr>
  <td>2021-09-12</td>
  <td>FID</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I want to keep only 30 days back using this column.</p>
  <p>I tried using <code>cast(my_date as date)</code> in the <code>where</code> clause, but it is not working.</p>
  <p>Can you assist?</p>
  <p>My code is in ANSI SQL.</p>