CREATE DATA Student
-- https://blog.csdn.net/mjb740074431/article/details/89375226
create table student
(sno varchar(8) PRIMARY KEY,
	sname VARCHAR(4) not null,
	ssex VARCHAR(2) default '男' check (ssex = '男' or ssex = '女'),
	sage int,
	sdept varchar(10)
);
SELECT * from student;

CREATE table course
(cno varchar(2) PRIMARY key,
	cname varchar(30),
	credit int,
	cpno varchar(3)
);
SELECT * from course;

create table sc
(sno varchar(8),
	cno varchar(2),
	grade int check(grade >=0 and grade <=100),
	primary key(sno,cno),
	foreign key(sno) references student(sno),
	foreign key(cno) references course(cno)
);
SELECT * from sc;

-- STUDENT表中增加一个字段入学时间scome，
alter table student add scome datetime;
-- 删除STUDENT表中sdept字段；
alter table student drop column sdept;
--  删除创建的SC表中cno字段和COURSE表cno字段之间的外键约束；
alter table sc drop constraint FK_sc_cno_182c9B23;
alter table sc drop constraint FK_sc_sno_173876EA;