sql 问题的求助

SELECT t1.name, t2.course_id, t2.count_class_session, t2.sum_duration, t4.id, t4.rowNo FROM `tb_course` t1 LEFT JOIN ( SELECT course_id, count(*) count_class_session, sum( duration ) sum_duration FROM tb_class_session GROUP BY course_id ) t2 ON t2.course_id = t1.id LEFT JOIN tb_learn_record t3 ON t3.course_id = t1.id LEFT JOIN ( SELECT a.id, ( @rowNum := @rowNum + 1 ) AS rowNo FROM tb_class_session a, ( SELECT ( @rowNum := 0 ) ) b ORDER BY a.sequence_no ASC ) t4 ON t4.id = t3.class_session_id 

求助 如何 把 t1.id 传入 SELECT a.id, ( @rowNum := @rowNum + 1 ) AS rowNo FROM tb_class_session a, ( SELECT ( @rowNum := 0 ) ) b ORDER BY a.sequence_no ASC 内