mysql 触发器实现级联删除有外键的多张表

2019-10-12 10:17:44

1、数据，建表时有可能会报错，只需要把前三行注释删掉就行

-- ----------------------------
-- Table structure for tb_grade
-- ----------------------------
DROP TABLE IF EXISTS `tb_grade`;
CREATE TABLE `tb_grade` (
  `grade_id` int(11) NOT NULL AUTO_INCREMENT,
  `grade_name` varchar(50) DEFAULT NULL,
  PRIMARY KEY (`grade_id`),
  UNIQUE KEY `grade_check` (`grade_name`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of tb_grade
-- ----------------------------
INSERT INTO `tb_grade` VALUES ('', '一年级');
INSERT INTO `tb_grade` VALUES ('', '二年级');
INSERT INTO `tb_grade` VALUES ('', '三年级');
INSERT INTO `tb_grade` VALUES ('', '四年级');
INSERT INTO `tb_grade` VALUES ('', '五年级');

-- ----------------------------
-- Table structure for tb_subject
-- ----------------------------
DROP TABLE IF EXISTS `tb_subject`;
CREATE TABLE `tb_subject` (
  `subject_id` int(11) NOT NULL AUTO_INCREMENT,
  `subject_name` varchar(20) DEFAULT NULL,
  `class_hour` int(3) DEFAULT NULL,
  `grade_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`subject_id`),
  KEY `grade_id` (`grade_id`),
  CONSTRAINT `tb_subject_ibfk_1` FOREIGN KEY (`grade_id`) REFERENCES `tb_grade` (`grade_id`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of tb_subject
-- ----------------------------
INSERT INTO `tb_subject` VALUES ('', 'java', '', '');
INSERT INTO `tb_subject` VALUES ('', 'html', '', '');
INSERT INTO `tb_subject` VALUES ('', 'javascript', '', '');
INSERT INTO `tb_subject` VALUES ('', 'database', '', '');
INSERT INTO `tb_subject` VALUES ('', 'java oop', '', '');
INSERT INTO `tb_subject` VALUES ('', 'servlet', '', '');
INSERT INTO `tb_subject` VALUES ('', 'jsp', '', '');
INSERT INTO `tb_subject` VALUES ('', 'struts2', '', '');
INSERT INTO `tb_subject` VALUES ('', 'hibernate', '', '');
INSERT INTO `tb_subject` VALUES ('', 'spring', '', '');

-- ----------------------------
-- Table structure for tb_student
-- ----------------------------
DROP TABLE IF EXISTS `tb_student`;
CREATE TABLE `tb_student` (
  `student_no` varchar(20) NOT NULL COMMENT '学号',
  `login_pwd` varchar(20) NOT NULL DEFAULT '' COMMENT '密码',
  `student_name` varchar(20) NOT NULL COMMENT '姓名',
  `sex` enum('女','男') DEFAULT '男' COMMENT '性别',
  `grade_id` int(11) DEFAULT NULL COMMENT '年级  - 外键',
  `phone` varchar(20) DEFAULT NULL COMMENT '联系电话',
  `address` varchar(100) DEFAULT '学生宿舍' COMMENT '现住址',
  `birthday` date DEFAULT NULL COMMENT '出生日期',
  `email` varchar(50) DEFAULT NULL COMMENT '电子邮件',
  PRIMARY KEY (`student_no`),
  KEY `grade_id` (`grade_id`),
  CONSTRAINT `tb_student_ibfk_1` FOREIGN KEY (`grade_id`) REFERENCES `tb_grade` (`grade_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of tb_student
-- ----------------------------
INSERT INTO `tb_student` VALUES ('s01', '', '宋江', '男', '', '', '学生宿舍', '1985-10-10', '13888811111@qq.com');
INSERT INTO `tb_student` VALUES ('s02', '', '卢俊义', '男', '', '', '教场西路8号', '1987-08-08', '13888822222@qq.com');
INSERT INTO `tb_student` VALUES ('s03', '', '吴用', '男', '', '', '教场西路8号', '1991-06-06', '13888833333@qq.com');
INSERT INTO `tb_student` VALUES ('s04', '', '孙二娘', '女', '', '', '教场西路16号', '1983-05-05', '13888844444@qq.com');
INSERT INTO `tb_student` VALUES ('s05', '', '李逵', '男', '', '', '学生宿舍', '1992-01-01', '13888855555@qq.com');
INSERT INTO `tb_student` VALUES ('s06', '', '顾大嫂', '女', '', '', '教场西路16号', '1990-02-02', '13888866666@qq.com');
INSERT INTO `tb_student` VALUES ('s07', '', '柴进', '男', '', '', '学生宿舍', '1991-03-03', null);
INSERT INTO `tb_student` VALUES ('s08', '', '林冲', '男', '', '', '教场西路8号', '1986-04-04', null);
INSERT INTO `tb_student` VALUES ('s09', '', '鲁智深', '男', '', '', '教场西路8号', '1991-05-05', '');
INSERT INTO `tb_student` VALUES ('s10', '', '扈三娘', '女', '', '', '学生宿舍', '1983-06-06', '');

-- ----------------------------
-- Table structure for tb_score
-- ----------------------------
DROP TABLE IF EXISTS `tb_score`;
CREATE TABLE `tb_score` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '成绩编号',
  `student_no` varchar(255) NOT NULL COMMENT '学号 - 外键',
  `subject_id` int(11) DEFAULT NULL COMMENT '所考科目',
  `student_score` float(5,2) DEFAULT '0.00' COMMENT '分数',
  `exam_date` date DEFAULT NULL COMMENT '考试日期',
  PRIMARY KEY (`id`),
  KEY `student_no` (`student_no`),
  KEY `subject_id` (`subject_id`),
  CONSTRAINT `tb_score_ibfk_1` FOREIGN KEY (`student_no`) REFERENCES `tb_student` (`student_no`),
  CONSTRAINT `tb_score_ibfk_2` FOREIGN KEY (`subject_id`) REFERENCES `tb_subject` (`subject_id`)
) ENGINE=InnoDB AUTO_INCREMENT=31 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of tb_score
-- ----------------------------
INSERT INTO `tb_score` VALUES ('', 's01', '', '90.50', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's02', '', '85.00', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's03', '', '69.50', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's04', '', '85.50', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's05', '', '45.50', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's06', '', '95.50', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's07', '', '76.50', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's08', '', '88.00', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's09', '', '70.00', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's10', '', '55.00', '2016-11-05');
INSERT INTO `tb_score` VALUES ('', 's01', '', '80.50', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's02', '', '70.00', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's03', '', '68.50', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's04', '', '82.50', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's05', '', '43.50', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's06', '', '90.50', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's07', '', '70.50', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's08', '', '80.00', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's09', '', '80.00', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's10', '', '56.00', '2016-11-07');
INSERT INTO `tb_score` VALUES ('', 's01', '', '84.50', '2016-11-09');
INSERT INTO `tb_score` VALUES ('', 's02', '', '73.00', '2016-11-09');
INSERT INTO `tb_score` VALUES ('', 's03', '', '69.50', '2016-11-09');
INSERT INTO `tb_score` VALUES ('', 's04', '', '86.50', '2016-11-09');
INSERT INTO `tb_score` VALUES ('', 's05', '', '44.50', '2016-11-09');
INSERT INTO `tb_score` VALUES ('', 's06', '', '80.50', '2016-11-09');
INSERT INTO `tb_score` VALUES ('', 's07', '', '75.50', '2016-11-09');
INSERT INTO `tb_score` VALUES ('', 's08', '', '87.00', '2016-11-09');
INSERT INTO `tb_score` VALUES ('', 's09', '', '85.00', '2016-11-09');
INSERT INTO `tb_score` VALUES ('', 's10', '', '66.00', '2016-11-09');

2、表结构

3、需求：针对数据库中的4张数据表(tb_grade、tb_subject、tb_student、tb_score)

在需要的数据表上创建触发器，达到每删除一个数据表的记录时都能顺顺利执行(级联删除)。

4、具体实现：

-- 为tb_grade创建触发器
DROP TRIGGER IF EXISTS trig_grade;
delimiter //
CREATE TRIGGER trig_grade BEFORE delete on tb_grade for each row
BEGIN
        DELETE FROM tb_student WHERE  grade_id = old.grade_id;
        DELETE FROM tb_subject WHERE grade_id = old.grade_id;
END //
delimiter ;

-- 为tb_student创建触发器
DROP TRIGGER IF EXISTS trig_student;
delimiter //
CREATE TRIGGER trig_student BEFORE delete on tb_student for each row
BEGIN
        DELETE FROM tb_score WHERE  student_no = old.student_no;
END //
delimiter ;

-- 为tb_subject创建触发器
DROP TRIGGER IF EXISTS trig_subject;
delimiter //
CREATE TRIGGER trig_subject BEFORE delete on tb_subject for each row
BEGIN
        DELETE FROM tb_score WHERE  subject_id = old.subject_id;
END //
delimiter ;

-- 查看此数据库中的触发器
SHOW TRIGGERS;

-- 测试删除数据是否能成功
DELETE FROM tb_student WHERE student_no = "S01";
DELETE FROM tb_grade WHERE grade_id = 1;
DELETE FROM tb_subject WHERE subject_id = 3;
DELETE FROM tb_score WHERE id = 9;

-- 最后可以查询表看看有没有被顺利删除

5、tb_score表是没有其他表将外键指向它的主键

想要删除从表的数据，需要先删除主表的数据