请问这个问题要怎么写呀

关系模型和完整性可以参考文章：
https://blog.csdn.net/hhhhxxn/article/details/105888468
https://blog.csdn.net/qq_42884482/article/details/100150177
参考答案如下（环境mysql）

create table s(
    sno varchar(10) primary key,
    sname varchar(20) not null,
    age int,
    sex int,
    dno varchar(10),
    foreign key(dno) references d(dno)
)

update sc set grade=grade +2 
where cno='C2'
    
delete from sc where sc.sno='S1'
    
select sno,sname from s where s.sno not in (select sno from sc)

select tno,tname from t where t.dno=(select dno from d where dname='信息')