/**
* Adds a group by to this query with named variables
* @param string $expression Group by expression
* @param array $variables Array with the variable name as key and the variable as value
* @return null
*/
public function addGroupByWithVariables($expression, array $variables)
{
$expression = $this->parseVariables($expression, $variables);
parent::addGroupByWithVariables($expression, array());
}
