title: MySQL Running Total return empty values
body: <pre><code>table values
  ------
  100
  50
  100
  50
  </code></pre>
  <pre><code>&lt;?php
  $sth = $DB-&gt;prepare('
      SELECT  ( @runnningtotal :=  @runnningtotal + values) FROM table 
      ');
  $sth-&gt;execute();
  
  
  print(&quot;All rows:\n&quot;);
  $result = $sth-&gt;fetchAll();
  print_r($result);
  ?&gt;
  </code></pre>
  <p>what is the problem on my code ? why @runnningtotal return empty values ?</p>