/**
* Adds "ON ..." conditions for the last created JOIN statement.
*
* @param mixed column name or array($column, $alias) or object
* @param string logic operator
* @param mixed column name or array($column, $alias) or object
* @return $this
*/
public function on($c1, $op, $c2)
{
return parent::on($this->_column($c1, TRUE), $op, $this->_column($c2, TRUE));
}
