CREATE TABLE course(
Course_id char(4) NOT NULL PRIMARY KEY COMMENT '课程号',
Course_name varchar(10) NOT NULL COMMENT '课程名',
credit tinyint(2) NOT NULL  COMMENT '学分',
stu_id char(15) NOT NULL  COMMENT '学号',
grade decimal(5,2) NOT NULL COMMENT '成绩',
t_id char(10) NOT NULL COMMENT '教师编号',
CONSTRAINT ct FOREIGN KEY (t_id)
REFERENCES teacher (t_id),CONSTRAINT cs FOREIGN KEY 
(stu_id)REFERENCES student (stu_id))