CREATE TABLE Student
(
Sno VARCHAR(9) PRIMARY KEY,   /*列级完整性约束条件，Sno是主码*/
Sname VARCHAR(20) UNIQUE,   /*Sname取唯一值*/
Ssex VARCHAR(2),
Sage SMALLINT,
Sdept VARCHAR(20)
);


CREATE TABLE Cour   se
(
Cno VARCHAR(4) PRIMARY KEY,
Cname VARCHAR(40),
Cpno VARCHAR(4),
Ccredit SMALLINT,
FOREIGN KEY(Cpno) REFERENCES Course(Cno)  /*表级完整性约束条件，Cpno是外码，被参照表是自身*/
);

CREATE TABLE SC
(
Sno VARCHAR(9),
Cno VARCHAR(4),
Grade SMALLINT,
PRIMARY KEY(Sno,Cno),
FOREIGN KEY(Sno) REFERENCES Student(Sno),
FOREIGN KEY(Cno) REFERENCES Course(Cno)
);

INSERT INTO Student (Sno,Sname,Ssex,Sdept,Sage) VALUES('201215121','李勇','男','CS',20);
INSERT INTO Student (Sno,Sname,Ssex,Sdept,Sage) VALUES('201215122','刘晨','女','CS',19);
INSERT INTO Student (Sno,Sname,Ssex,Sdept,Sage) VALUES('201215123','王敏','女','MA',18);
INSERT INTO Student (Sno,Sname,Ssex,Sdept,Sage) VALUES('201215125','张立','男','IS',19);
INSERT INTO Student (Sno,Sname,Ssex,Sdept,Sage) VALUES('201215128','陈冬','男','IS',20);

SELECT * FROM Student

INSERT INTO Course(Cno,Cname,Cpno,Ccredit) VALUES('1','数据库',NULL,4);
INSERT INTO Course(Cno,Cname,Cpno,Ccredit) VALUES('2','数学',NULL,4);
INSERT INTO Course(Cno,Cname,Cpno,Ccredit) VALUES('3','信息系统',NULL,4);
INSERT INTO Course(Cno,Cname,Cpno,Ccredit) VALUES('4','操作系统',NULL,4);
INSERT INTO Course(Cno,Cname,Cpno,Ccredit) VALUES('5','数据结构',NULL,4);
INSERT INTO Course(Cno,Cname,Cpno,Ccredit) VALUES('6','数据处理',NULL,4);
INSERT INTO Course(Cno,Cname,Cpno,Ccredit) VALUES('7','Pascal语言',NULL,4);

UPDATE Course SET Cpno='5' WHERE Cno='1'
UPDATE Course SET Cpno='1' WHERE Cno='3'
UPDATE Course SET Cpno='6' WHERE Cno='4'
UPDATE Course SET Cpno='7' WHERE Cno='5'
UPDATE Course SET Cpno='8' WHERE Cno='7'

SELECT * FROM Course

INSERT INTO SC(Sno,Cno,Grade) VALUES ('201215121','1',92);
INSERT INTO SC(Sno,Cno,Grade) VALUES ('201215121','2',85);
INSERT INTO SC(Sno,Cno,Grade) VALUES ('201215121','3',88);
INSERT INTO SC(Sno,Cno,Grade) VALUES ('201215122','2',90);
INSERT INTO SC(Sno,Cno,Grade) VALUES ('201215122','3',80);

SELECT *FROM SC