title: PHP: Variable empty or not set or what?
body: <p>What is the difference between these four PHP statements?</p>
  
  <pre><code>if (isset($data)) {
  
  if (!empty($data)) {
  
  if ($data != '') {
  
  if ($data) {
  </code></pre>
  
  <p>Do they all do the same?</p>