public function query($sql)
    {
        // get start time of sql execution
        $start = $this->_firebug->timer();
        // execute sql
        $records = $this->_pdo->query($sql);
        // record sql statement
        if ($this->_firebug->isEnabled()) {
            $trace = debug_backtrace();
            $this->_recordSqlStatement($start, $sql, $trace);
        }

        return $records;
    }