mysql的自增序号实现

SELECT cast(@rank := @rank+1 as char) as rowNum,a.* from

(select oup.user_name as userName,oup.user_id as userId,oup.student_sex as studentSex,op.Introduction,op.create_time as createTime,oup.score, oup.type from order_user_paper oup left join order_paper op on oup.paper_id = op.id
where oup.paper_id = 1 and user_id in (select user_id from t_student where class_id = 119) and oup.type = 2 ) a
left join ( SELECT @rank :=0 ) b on 1 = 1