use student_class
create table SC
(sclass varchar(2),--班級
sno varchar(2),--編號
cno varchar(3),--課程號
grade real check(grade<=100.0 and grade>=0.0), --成績
primary key(sclass,sno,cno),
foreign key (cno) references Course (cno),
foreign key (sno,sclass) references Student(sno,sclass)
)
insert into SC(Sclass,Sno,Cno,grade)
values(1,1,1,92)  
insert into SC(Sclass,Sno,Cno,grade)
values(1,1,2,85)  
insert into SC(Sclass,Sno,Cno,grade)
values(1,1,3,88)  
insert into SC(Sclass,Sno,Cno,grade)
values(1,2,2,90)  
insert into SC(Sclass,Sno,Cno,grade)
values(1,2,3,80)  
insert into SC(Sclass,Sno,Cno,grade)
values(2,1,1,75)  
insert into SC(Sclass,Sno,Cno,grade)
values(2,1,2,92)  
insert into SC(Sclass,Sno,Cno,grade)
values(2,2,2,87)  
insert into SC(Sclass,Sno,Cno,grade)
values(2,2,3,89)  
insert into SC(Sclass,Sno,Cno,grade)
values(2,3,1,90)