title: How to sort php array by multiple fields using usort
body: <pre><code>usort($childs, function($a, $b) {
      return $a['parent_id'] - $b['parent_id'];
  });
  </code></pre>
  
  <p>Here I'm sorting it by 1 field, how can I add more fields to sort them?, Like if it was the <code>ORDER BY field1, field2, field3</code> in Mysql</p>