insert into s1 select 作者姓名,count(作者姓名) as 图书统计 from author inner join books on author.authorid=books.authorid group by 作者姓名 having count(作者姓名)>=3select left(学号,4) as 年级, 课程id,avg(成绩) as 平均分 from tGradegroup by left(学号,4),课程id order by left(学号,4) desc