TYPO3 GROUP BY Returns false.

$result = $GLOBALS['TYPO3_DB']->exec_SELECTquery(
                'uid,question,reply,full_name,email', // SELECT
                $this->dbExportTable, // FROM
                '1=1 AND pid ="' . $pid . '"', // WHERE
                'question,email,reply', // GROUP BY
                '', // ORDER BY
                ''// LIMIT
        );