作业练习：
http://www.cnblogs.com/wupeiqi/articles/5729934.html制表语句：
制表语句： 班级表 Table: class Create Table: CREATE TABLE `class` ( `cid` int(11) NOT NULL AUTO_INCREMENT, `caption` varchar(50) DEFAULT NULL, PRIMARY KEY (`cid`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 1 row in set (0.00 sec) 学生表： Table: student Create Table: CREATE TABLE `student` ( `sid` int(11) NOT NULL AUTO_INCREMENT, `sname` varchar(50) DEFAULT NULL, `gender` char(10) DEFAULT NULL, `class_id` int(11) DEFAULT NULL, PRIMARY KEY (`sid`), KEY `fk_student_class` (`class_id`), CONSTRAINT `fk_student_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 老师表： Table: teacher Create Table: CREATE TABLE `teacher` ( `tid` int(11) NOT NULL AUTO_INCREMENT, `tname` varchar(50) DEFAULT NULL, PRIMARY KEY (`tid`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 1 row in set (0.00 sec) 课程表： Table: course Create Table: CREATE TABLE `course` ( `cid` int(11) NOT NULL AUTO_INCREMENT, `cname` char(25) DEFAULT NULL, `teacher_id` int(11) DEFAULT NULL, PRIMARY KEY (`cid`), KEY `fk_course_teacher` (`teacher_id`), CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 1 row in set (0.00 sec) 成绩表： create table score (sid int not null auto_increment primary key, student_id int not null, corse_id int not null, number int not null, unique uq_sc (student_id,corse_id), CONSTRAINT fk_sc_st FOREIGN key (student_id) REFERENCES student(sid), constraint fk_sc_co foreign key (corse_id) references course(cid) ) engine=innodb default charset=utf8;