创建Student表

CREATE TABLE Student (
	Sno CHAR(7) PRIMARY KEY,
	Sname CHAR(10) NOT NULL,
	Ssex CHAR(2),
	Sage TINYINT,
	Sdept CHAR(20)
)

创建Course表

CREATE TABLE Course(
	Cno CHAR(6) NOT NULL PRIMARY KEY,
	Cname CHAR(20) NOT NULL,
	Credit TINYINT,
	Semester TINYINT,
)

创建SC表

CREATE TABLE SC(
	Sno CHAR(7) NOT NULL,
	Cno CHAR(6) NOT NULL,
	Grade SMALLINT,
	PRIMARY KEY(Sno,Cno),
	FOREIGN	KEY(Sno) REFERENCES Student(Sno),
	FOREIGN KEY(Cno) REFERENCES Course(Cno)

)

创建Student表数据

INSERT INTO Student
VALUES('1512101','李勇','男',19,'计算机系'),('1512102','刘晨','男',20,'计算机系'),
('1512103','王敏','女',18,'计算机系'),('1512104','李小玲','女',19,'计算机系'),('1521101','张立','男',22,'信息系'),
('1521102','吴宾','女',21,'信息系'),('1521103','张海','男',20,'信息系'),('1531101','钱小平','女',18,'数学系'),
('1531102','王大力','男',19,'数学系')

创建Course表数据

INSERT INTO Course
VALUES('c001','计算机文化学',3,1),('c002','高等数学',6,1),('c003','高等数学',3,2),
('c004','大学英语',6,2),('c005','Java',2,3),('c006','程序设计',3,3),
('c007','数据结构',5,4),('c008','操作系统',4,4),('c009','数据库基础',4,5),
('c010','计算机网络',5,6)

创建SC表数据 有问题

INSERT INTO SC
VALUES('1512101','c001',90),('1512101','c002',86),('1512101','c003',92),('1512101','c005',88),('1512101','c006',NULL),
('1512102','c001',76),('1512102','c002',78),('1512102','c005',66),
('1512104','c002',66),('1512104','c005',78),('1512104','c008',66),
('1521102','c001',82),('1521102','c005',75),('1521102','c007',92),('1521102','c009',50),
('1521103','c002',68),('1521103','c006',NULL),('1521103','c007',NULL),('1521103','c008',78),
('1531101','c001',80),('1531101','c005',50),('1531101','c007',45),
('1531102','c001',80),('1531102','c002',75),('1531102','c005',85),('1531102','c009',88)