1.筛选成绩表分数在60（包括60）
select * from 成绩表 where 成绩 >=60
2.按学号分组,按条件过滤
select t1.学号, count(t1.课程号),avg(t1.成绩) from (select * from 成绩表 where 成绩 >=60) t1 group by t1.学号 having avg(t1.成绩) >=70 amd count(t1.课程号) >=2

select t1.学号, count(t1.课程号),avg(t1.成绩) from (select * from 成绩表 where 成绩 >=60) t1 group by t1.学号 having avg(t1.成绩) >=70 amd count(t1.课程号) >=2