Leilões em destaque acontencendo

SQLSTATE[42000]: Syntax error or access violation: 1055 Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'leilaoq_db.a.course_id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

SELECT a.*, b.*, c.* FROM tbl_course a, tbl_course_cron b, tbl_category c WHERE a.course_id = b.course_id AND a.category_id = c.category_id AND a.course_rascunho = 0 AND a.course_encerrado = 0 AND a.course_auditado = 0 GROUP BY c.category_id