//学生表创建
CREATE table student(
Sno CHAR(9) PRIMARY KEY,
Sname CHAR(20) UNIQUE,
Ssex char(2),
Sage SMALLINT,
Sdept char(20)
);

//课程表创建
CREATE table course(
Cno char(4) PRIMARY KEY,
Cname char(40) not NULL,
Cpno char(4),
Ccredit SMALLINT
);

//学生选课表创建
CREATE table SC(
Sno char(9),
Cno char(4),
Grade SMALLINT
);