分组计算平均成绩

11.查询每门课的平均成绩

select avg(degree) from score where c_no='3-105';
select avg(degree) from score where c_no='3-245';
select avg(degree) from score where c_no='6-166';

但我们可以建立分组来简化计算；

select c_no,avg(degree) from score group by c_no;