一个学生成绩管理系统的代码

    数据库结构为：
DROP DATABASE IF EXISTS ENOVA;
CREATE DATABASE ENOVA;
USE ENOVA;

CREATE TABLE STUDENT (
    ID int(11) NOT NULL auto_increment,
    NUMBER char(15) NOT NULL UNIQUE,
    NAME varchar(4) NOT NULL ,
    SEX varchar(1) default NULL,
    NATION varchar(10) default NULL,
    ENROLL_YEAR YEAR(4) NOT NULL ,
    BIRTHDAY date default NULL,
    BIRTH_PLACE varchar(50) default NULL,
    PASSWORD char(15) NOT NULL ,
    CLASS_ID int(11) NOT NULL ,
    PRIMARY KEY  (ID))ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE TEACHER(
    ID int(11) NOT NULL auto_increment,
    NAME varchar(4) default NULL ,
    SEX varchar(1) default NULL,
    USERNAME char(15) NOT NULL UNIQUE ,
    PASSWORD char(15) NOT NULL ,
    PRIMARY KEY  (ID))ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE DEPARTMENT(
    ID int(11) NOT NULL auto_increment,
    NAME varchar(20) NOT NULL,
    PRIMARY KEY (ID))ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE SPECIAL(
    ID int(11) NOT NULL auto_increment,
    NAME varchar(20) NOT NULL,
    DEPARTMENT_ID int(11) NOT NULL ,
    PRIMARY KEY (ID))ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE CLASS(
    ID int(11) NOT NULL auto_increment,
    NAME varchar(20) NOT NULL,
    TEACHER_ID int(11) NOT NULL ,
    SPECIAL_ID int(11) NOT NULL ,
    YEAR year(4) NOT NULL ,
    PRIMARY KEY (ID))ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE COURSE(
    ID int(11) NOT NULL auto_increment,
    NAME varchar(20) NOT NULL,
    TEACHER_ID int(11) NOT NULL ,
    HOUR int(4) default NULL,
    CREDIT float(2,1) NOT NULL ,
    YEAR year(4) default NULL,
    TERM varchar(1) default NULL,
    EXAM_MODE varchar(2) default NULL,
    EXAM_TYPE varchar(2) default NULL,
    TYPE varchar(2) default NULL,
    PRIMARY KEY  (ID))ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE SCORE(
    COURSE_ID int(11) NOT NULL ,
    STUDENT_ID int(11) NOT NULL ,
    VALUE int(4) default NULL ,
    DATE date NOT NULL ,
    PRIMARY KEY  (STUDENT_ID,COURSE_ID))ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE ROOT(
    ID int(11) NOT NULL auto_increment,
    USERNAME char(15) NOT NULL UNIQUE ,
    PASSWORD char(15) NOT NULL ,
    PRIMARY KEY (ID))ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE CLASS_COURSE(
    CLASS_ID int(11) NOT NULL ,
    COURSE_ID int(11) NOT NULL ,
    PRIMARY KEY (CLASS_ID,COURSE_ID))ENGINE=InnoDB DEFAULT CHARSET=utf8;

alter table STUDENT add constraint FK_STUDENT_CLASS
      foreign key(CLASS_ID) references CLASS(ID) on delete cascade;

alter table SPECIAL add constraint FK_SPECIAL_DEPARTMENT
      foreign key(DEPARTMENT_ID) references DEPARTMENT(ID) on delete cascade;

alter table CLASS add constraint FK_CLASS_TEACHER
      foreign key(TEACHER_ID) references TEACHER(ID) on delete cascade;

alter table CLASS add constraint FK_CLASS_SPECIAL
      foreign key(SPECIAL_ID) references SPECIAL(ID) on delete cascade;

alter table SCORE add constraint FK_SCORE_COURSE
      foreign key(COURSE_ID) references COURSE(ID) on delete cascade;

alter table SCORE add constraint FK_SCORE_SUTDENT
      foreign key(STUDENT_ID) references STUDENT(ID) on delete cascade;

alter table CLASS_COURSE add constraint FK_CC_CLASS
      foreign key(CLASS_ID) references CLASS(ID) on delete cascade;

alter table CLASS_COURSE add constraint FK_CC_COURSE
      foreign key(COURSE_ID) references COURSE(ID) on delete cascade;