Mysql 5.7 support Q&A plugin

SQL ERROR [ mysqli ]

Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'phpbb.q.question_id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by [1055]

$sql = 'SELECT q.question_id, q.lang_iso

            FROM ' . $this->table_captcha_questions . ' q, ' . $this->table_captcha_answers . ' a

            WHERE q.question_id = a.question_id';

            GROUP BY lang_iso';