Question

用SQL语句表示下列问题？

Answer 1

1、select name,count(class) from student_score sc left join student_info si on sc.id=si.id
GROUP BY name
HAVING count(class) =1;

2、select class,count(id) from student_info si GROUP BY class;

3、select name,count(class) as '选修课程',avg(score) as '每门平均',sum(score) as '所选总分' from student_score sc left join student_info si on sc.id=si.id