在一个成绩管理系统数据库GradeDB中，定义如下关系表： STUDENT(SID,SName,Age,Sex) GRADE(SID,CID,Score, Note) COURSE(CID,CName,Teacher) （1）编写SQL程序创建数据库及其关系表，并插入20个学生的2门课程（“数据库原理及应用”、“数据结构与算法”）成绩数据； （2）GradeLOG表的信息包括user操作用户、SID学号、CID课程号、changetime修改时间、oldscore修改前成绩、newscore修改后成绩。 创建GradeLOG表。 编写触发器程序实现GRADE表数据的插入、删除、修改在日志表（GradeLOG）记录相关操作数据，如操作用户、学号、课程号、修改时间、修改前成绩、修改后成绩。 （3）编写存储过程程序实现统计各课程不及格学生人数，并在屏幕输出；

（1）创建数据库及其关系表，并插入数据：

CREATE DATABASE GradeDB;

USE GradeDB;

CREATE TABLE STUDENT (
    SID CHAR(10) PRIMARY KEY,
    SName VARCHAR(20) NOT NULL,
    Age INT NOT NULL,
    Sex CHAR(2) NOT NULL
);

CREATE TABLE COURSE (
    CID CHAR(10) PRIMARY KEY,
    CName VARCHAR(20) NOT NULL,
    Teacher VARCHAR(20) NOT NULL
);

CREATE TABLE GRADE (
    SID CHAR(10) REFERENCES STUDENT(SID),
    CID CHAR(10) REFERENCES COURSE(CID),
    Score INT NOT NULL,
    Note VARCHAR(50),
    PRIMARY KEY (SID, CID)
);

INSERT INTO STUDENT VALUES ('200001', '张三', 19, '男');
INSERT INTO STUDENT VALUES ('200002', '李四', 20, '女');
INSERT INTO STUDENT VALUES ('200003', '王五', 18, '男');
INSERT INTO STUDENT VALUES ('200004', '赵六', 21, '女');
INSERT INTO STUDENT VALUES ('200005', '刘七', 20, '男');
INSERT INTO STUDENT VALUES ('200006', '陈八', 19, '女');
INSERT INTO STUDENT VALUES ('200007', '张九', 18, '男');
INSERT INTO STUDENT VALUES ('200008', '李十', 21, '女');
INSERT INTO STUDENT VALUES ('200009', '王麻子', 20, '男');
INSERT INTO STUDENT VALUES ('200010', '赵大', 19, '女');
INSERT INTO STUDENT VALUES ('200011', '刘二', 18, '男');
INSERT INTO STUDENT VALUES ('200012', '陈三', 21, '女');
INSERT INTO STUDENT VALUES ('200013', '张四', 20, '男');
INSERT INTO STUDENT VALUES ('200014', '李五', 19, '女');
INSERT INTO STUDENT VALUES ('200015', '王六', 18, '男');
INSERT INTO STUDENT VALUES ('200016', '赵七', 21, '女');
INSERT INTO STUDENT VALUES ('200017', '刘八', 20, '男');
INSERT INTO STUDENT VALUES ('200018', '陈九', 19, '女');
INSERT INTO STUDENT VALUES ('200019', '张十', 18, '男');
INSERT INTO STUDENT VALUES ('200020', '李一', 21, '女');

INSERT INTO COURSE VALUES ('C001', '数据库原理及应用', '张三');
INSERT INTO COURSE VALUES ('C002', '数据结构与算法', '李四');

INSERT INTO GRADE VALUES ('200001', 'C001', 80, '优秀');
INSERT INTO GRADE VALUES ('200001', 'C002', 75, '良好');
INSERT INTO GRADE VALUES ('200002', 'C001', 65, '及格');
INSERT INTO GRADE VALUES ('200002', 'C002', 70, '良好');
INSERT INTO GRADE VALUES ('200003', 'C001', 55, '不及格');
INSERT INTO GRADE VALUES ('200003', 'C002', 60, '及格');
INSERT INTO GRADE VALUES ('200004', 'C001', 90, '优秀');
INSERT INTO GRADE VALUES ('200004', 'C002', 85, '优秀');
INSERT INTO GRADE VALUES ('200005', 'C001', 70, '良好');
INSERT INTO GRADE VALUES ('200005', 'C002', 75, '良好');
INSERT INTO GRADE VALUES ('200006', 'C001', 80, '优秀');
INSERT INTO GRADE VALUES ('200006', 'C002', 85, '优秀');
INSERT INTO GRADE VALUES ('200007', 'C001', 60, '及格');
INSERT INTO GRADE VALUES ('200007', 'C002', 65, '及格');
INSERT INTO GRADE VALUES ('200008', 'C001', 75, '良好');
INSERT INTO GRADE VALUES ('200008', 'C002', 80, '优秀');
INSERT INTO GRADE VALUES ('200009', 'C001', 55, '不及格');
INSERT INTO GRADE VALUES ('200009', 'C002', 60, '及格');
INSERT INTO GRADE VALUES ('200010', 'C001', 70, '良好');
INSERT INTO GRADE VALUES ('200010', 'C002', 75, '良好');

（2）创建GradeLOG表，并编写触发器程序实现GRADE表数据的插入、删除、修改在日志表记录相关操作数据：

CREATE TABLE GradeLOG (
    user VARCHAR(20),
    SID CHAR(10),
    CID CHAR(10),
    changetime DATETIME,
    oldscore INT,
    newscore INT
);

DELIMITER $$
CREATE TRIGGER log_insert
AFTER INSERT ON GRADE
FOR EACH ROW
BEGIN
    INSERT INTO GradeLOG VALUES (USER(), NEW.SID, NEW.CID, NOW(), NULL, NEW.Score);
END$$

CREATE TRIGGER log_delete
AFTER DELETE ON GRADE
FOR EACH ROW
BEGIN
    INSERT INTO GradeLOG VALUES (USER(), OLD.SID, OLD.CID, NOW(), OLD.Score, NULL);
END$$

CREATE TRIGGER log_update
AFTER UPDATE ON GRADE
FOR EACH ROW
BEGIN
    INSERT INTO GradeLOG VALUES (USER(), NEW.SID, NEW.CID, NOW(), OLD.Score, NEW.Score);
END$$
DELIMITER ;

-- 测试触发器
DELETE FROM GRADE WHERE SID = '200001' AND CID = 'C001';
UPDATE GRADE SET Score = 90 WHERE SID = '200002' AND CID = 'C002';

（3）编写存储过程程序实现统计各课程不及格学生人数，并在屏幕输出：

DELIMITER $$
CREATE PROCEDURE count_failed_students()
BEGIN
    DECLARE c_name VARCHAR(20);
    DECLARE c_id CHAR(10);
    DECLARE n INT;
    DECLARE done INT DEFAULT FALSE;
    
    DECLARE cur1 CURSOR FOR SELECT CName, CID FROM COURSE;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
    
    OPEN cur1;
    
    read_loop: LOOP
        FETCH cur1 INTO c_name, c_id;
        IF done THEN
            LEAVE read_loop;
        END IF;
        
        SELECT COUNT(*) INTO n FROM GRADE WHERE CID = c_id AND Score < 60;
        SELECT CONCAT(c_name, '不及格人数为', n) AS Result;
    END LOOP;
    
    CLOSE cur1;
END$$
DELIMITER ;

-- 执行存储过程
CALL count_failed_students();

以上代码是一个完整的MySQL数据库程序，可以创建数据库、关系表、插入数据、创建触发器和存储过程，实现对学生成绩的管理。