A.select * from class B.drop * from class C.modify * from class D.change * from class
A.select * from student order by named esc B.select * from student order by name asc C.select * from student group by named esc D.select * from student group by name
A.select avg(score)from stu B.select max(score)from stu C.select min(score)from stu D.select sum(score)from stu