public function constructSelectSQL($fields)
    {
        $sql = array();

        $sql[] = "SELECT";

        $sql[] = "`" . implode("`, `", array_keys($fields)) . "`";

        $sql[] = "FROM `" . $this->dbtable . "`";
        $sql[] = "WHERE `" . $this->pk . "` = " . $fields[$this->pk]->getSQL();

        return implode(" ", $sql);
    }