1. 触发器介绍

触发器是与表有关的数据库对象，指在insert / update / delete之前(BEFORE)或之后(AFTER)，触发并执行触发器中定义的SQL语句集合。触发器的这种特性可以协助应用在数据库端确保数据的完整性，日志记录，数据校验等操作 。

使用别名OLD和NEW来引用触发器中发生变化的记录内容，这与其他的数据库是相似的。现在触发器还只支持行级触发，不支持语句级触发。

触发器类型	NEW 和 OLD
INSERT 型触发器	NEW 表示将要或者已经新增的数据
UPDATE 型触发器	OLD 表示修改之前的数据，NEW 表示将要或已经修改后的数据
DELETE 型触发器	OLD 表示将要或者已经删除的数据

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2. 触发器语法

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2.1 创建触发器

CREATE TRIGGER trigger_name
BEFORE/AFTER INSERT/UPDATE/DELETE
ON tbl_name FOR EACH ROW -- 行级触发器
BEGIN
	trigger_stmt;
END;

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2.2 查看触发器

SHOW TRIGGERS;

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2.3 删除触发器

-- 如果没有指定 schema_name，默认为当前数据库
DROP TRIGGER [schema_name.]trigger_name ; 

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3. 触发器案例

通过触发器记录 tb_user 表的数据变更日志，将变更日志插入到日志表user_logs中, 包含增加、修改、删除；

表结构准备:

-- 准备工作 : 日志表 user_logs
create table user_logs
(
    id             int(11)     not null auto_increment,
    operation      varchar(20) not null comment '操作类型, insert/update/delete',
    operate_time   datetime    not null comment '操作时间',
    operate_id     int(11)     not null comment '操作的ID',
    operate_params varchar(500) comment '操作参数',
    primary key (`id`)
) engine = innodb
  default charset = utf8;

示例数据准备：

create table tb_user
(
    id         int primary key auto_increment comment '主键',
    name       varchar(50) not null comment '用户名',
    phone      varchar(11) not null comment '手机号',
    email      varchar(100) comment '邮箱',
    profession varchar(11) comment '专业',
    age        tinyint unsigned comment '年龄',
    gender     char(1) comment '性别 , 1: 男, 2: 女',
    status     char(1) comment '状态',
    createtime datetime comment '创建时间'
) comment '系统用户表';

INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('吕布', '17799990000', '[email protected]', '软件工程', 23, '1', '6', '2001-02-02 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('曹操', '17799990001', '[email protected]', '通讯工程', 33, '1', '0', '2001-03-05 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('赵云', '17799990002', '[email protected]', '英语', 34, '1', '2', '2002-03-02 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('孙悟空', '17799990003', '[email protected]', '工程造价', 54, '1', '0', '2001-07-02 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('花木兰', '17799990004', '[email protected]', '软件工程', 23, '2', '1', '2001-04-22 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('大乔', '17799990005', '[email protected]', '舞蹈', 22, '2', '0', '2001-02-07 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('露娜', '17799990006', '[email protected]', '应用数学', 24, '2', '0', '2001-02-08 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('程咬金', '17799990007', '[email protected]', '化工', 38, '1', '5', '2001-05-23 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('项羽', '17799990008', '[email protected]', '金属材料', 43, '1', '0', '2001-09-18 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('白起', '17799990009', '[email protected]', '机械工程及其自动 化', 27, '1', '2', '2001-08-16 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('韩信', '17799990010', '[email protected]', '无机非金属材料工 程', 27, '1', '0', '2001-06-12 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('荆轲', '17799990011', '[email protected]', '会计', 29, '1', '0', '2001-05-11 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('兰陵王', '17799990012', '[email protected]', '工程造价', 44, '1', '1', '2001-04-09 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('狂铁', '17799990013', '[email protected]', '应用数学', 43, '1', '2', '2001-04-10 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('貂蝉', '17799990014', '[email protected]', '软件工程', 40, '2', '3', '2001-02-12 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('妲己', '17799990015', '[email protected]', '软件工程', 31, '2', '0', '2001-01-30 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('芈月', '17799990016', '[email protected]', '工业经济', 35, '2', '0', '2000-05-03 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('嬴政', '17799990017', '[email protected]', '化工', 38, '1', '1', '2001-08-08 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('狄仁杰', '17799990018', '[email protected]', '国际贸易', 30, '1', '0', '2007-03-12 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('安琪拉', '17799990019', '[email protected]', '城市规划', 51, '2', '0', '2001-08-15 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('典韦', '17799990020', '[email protected]', '城市规划', 52, '1', '2', '2000-04-12 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('廉颇', '17799990021', '[email protected]', '土木工程', 19, '1', '3', '2002-07-18 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('后羿', '17799990022', '[email protected]', '城市园林', 20, '1', '0', '2002-03-10 00:00:00');
INSERT INTO tb_user (name, phone, email, profession, age, gender, status, createtime)
VALUES ('姜子牙', '17799990023', '[email protected]', '工程造价', 29, '1', '4', '2003-05-26 00:00:00');

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3.1 插入数据触发器

create trigger tb_user_insert_trigger
    after insert
    on tb_user
    for each row
begin
    insert into user_logs(id, operation, operate_time, operate_id, operate_params)
    VALUES (null, 'insert', now(), new.id,
            concat('插入的数据内容为: id=', new.id, ',name=', new.name, ', phone=', NEW.phone, ', email=', NEW.email,
                   ', profession=', NEW.profession));
end;

测试：

-- 查看
show triggers;

-- 插入数据到tb_user
insert into tb_user(id, name, phone, email, profession, age, gender, status, createtime)
VALUES (26, '二皇子', '18809091212', '[email protected]', '软件工程', 23, '1', '1', now());

查看user_logs里面的数据

测试完毕之后，检查日志表中的数据是否可以正常插入，以及插入数据的正确性。

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3.2 修改数据触发器

create trigger tb_user_update_trigger
    after update
    on tb_user
    for each row
begin
    insert into user_logs(id, operation, operate_time, operate_id, operate_params)
    VALUES (null, 'update', now(), new.id,
            concat('更新之前的数据: id=', old.id, ',name=', old.name, ', phone=', old.phone, ', email=', old.email,
                   ', profession=', old.profession, ' | 更新之后的数据: id=', new.id, ',name=', new.name, ', phone=',
                   NEW.phone, ', email=', NEW.email, ', profession=', NEW.profession));
end;

-- 查看
show triggers;

-- 更新
update tb_user
set profession = '会计'
where id = 23;

update tb_user
set profession = '会计'
where id <= 5;

测试完毕之后，检查日志表中的数据是否可以正常插入，以及插入数据的正确性。

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3.3 删除数据触发器

create trigger tb_user_delete_trigger
    after delete
    on tb_user
    for each row
begin
    insert into user_logs(id, operation, operate_time, operate_id, operate_params)
    VALUES (null, 'delete', now(), old.id,
            concat('删除之前的数据: id=', old.id, ',name=', old.name, ', phone=', old.phone, ', email=', old.email,
                   ', profession=', old.profession));
end;

查看新增的删除数据触发器：

show triggers;

-- 删除数据
delete
from tb_user
where id = 26;

测试完毕之后，检查日志表中的数据是否可以正常插入，以及插入数据的正确性。

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4. 小结

• MySQL视图
• MySQL 存储过程 存储函数

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