/**
  * Returns the current sql version of the database.
  * 
  * @return	string
  */
 public function getSQLVersion()
 {
     if ($this->sqlVersion === null) {
         try {
             $this->sqlVersion = $this->db->getVersion();
         } catch (DatabaseException $e) {
             $this->sqlVersion = 'unknown';
         }
     }
     return $this->sqlVersion;
 }