select StudentNo 学号,AVG(StudentResult) 平均分
from Result
group by StudentNo
having AVG(StudentResult)>=90
--每名学生的4科成绩的平均分取90分以上

120页4 5题
select c_ID 会员号,SUM(o_Sum) 下单总额
from Orders
group by c_ID
having SUM(o_Sum)>AVG(o_Sum)
select o_Date 下单日期,SUM (o_Sum) 下单总额
from Orders
group by o_Date
order by SUM (o_Sum) desc