title: check results between two dates or null
body: <p>I have no idea about how to search for rows between two dates and the case where the start date or end date are null.</p>
  <p><strong>Here what I have done:</strong></p>
  <pre><code>SELECT * FROM results WHERE ((start_date &gt;= $start_date AND end_date &lt;= $end_date) OR '$end_date'='' OR '$start_date'='')
  </code></pre>
  <p>But not a working example.</p>