假期闲的慌，不如做一点SQL基础练习吧

[1]select sum(成绩)
from score
where 课程号='0002'

[2]select count(distinct 学号) as 学生人数
from score

[1]select 课程号,max(成绩) as 最高分,min(成绩) as 最低分 
from score
group by 课程号

[2]select 课程号,count(学号)
from score
group by 课程号

[3]select 性别,count(*)
from student
group by 性别

[1]select 学号,average(成绩)
from score
group by 学号
having  avg(成绩)>60;
[2]select 学号,count(课程号) as 选修课程数目
from score
group by 学号
having count(课程号) >=2;
[3]select 姓名,count(*) as 人数
from student
group by 姓名
having count(*)>=2;

select 课程号,avg(成绩)
from socre
group by 课程号
having avg(成绩)>=80;

[1]select 课程号
from score
where 成绩<60
order by 课程号 desc;
[2]
select 课程号,avg(成绩) as 平均成绩
from score
group by 课程号
order by 平均成绩 asc,课程号 desc;

select 学号
from score
where 课程编号=‘04’ and 成绩<60
order by 分数 desc;

select 课程号,count(学号) as '学生选修人数'
from score
group by 课程号
having count(学号)>2
order by 学生选修人数 desc,课程号 asc;

select 学号,avg(成绩)
from score
where 成绩<60 
group by 学号
having count(学号)>2