480 lines
14 KiB
Markdown
480 lines
14 KiB
Markdown
### 语法结构
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```sql
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DELIMITER //
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CREATE TRIGGER trigger_name
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{BEFORE | AFTER} {INSERT | UPDATE | DELETE} ON table_name
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FOR EACH ROW
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BEGIN
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-- 触发器的逻辑代码
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-- 可以包含 SQL 语句、流程控制语句（如 IF、CASE 等）、变量声明等
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END//
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DELIMITER ;
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```
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### 表结构和数据
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```sql
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-- 创建数据库
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CREATE DATABASE company CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
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-- 使用数据库
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USE company;
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-- 创建 department 表
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CREATE TABLE department (
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dept_id INT AUTO_INCREMENT PRIMARY KEY COMMENT '部门ID，主键',
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dept_name VARCHAR(100) NOT NULL COMMENT '部门名称',
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location VARCHAR(100) NOT NULL COMMENT '部门所在地'
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);
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-- 创建 job 表
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CREATE TABLE job (
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job_id INT AUTO_INCREMENT PRIMARY KEY COMMENT '职位ID，主键',
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job_title VARCHAR(100) NOT NULL COMMENT '职位名称',
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min_salary DECIMAL(10, 2) NOT NULL COMMENT '最低工资',
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max_salary DECIMAL(10, 2) NOT NULL COMMENT '最高工资'
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);
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-- 创建 employee 表
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CREATE TABLE employee (
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emp_id INT AUTO_INCREMENT PRIMARY KEY COMMENT '员工ID，主键',
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emp_name VARCHAR(100) NOT NULL COMMENT '员工姓名',
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salary DECIMAL(10, 2) NOT NULL COMMENT '员工工资',
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hire_date DATE NOT NULL COMMENT '入职日期',
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dept_id INT COMMENT '部门ID，外键',
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job_id INT COMMENT '职位ID，外键',
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FOREIGN KEY (dept_id) REFERENCES department(dept_id),
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FOREIGN KEY (job_id) REFERENCES job(job_id)
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);
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INSERT INTO department (dept_name, location) VALUES
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('HR', 'New York'),
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('IT', 'San Francisco'),
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('Finance', 'Chicago'),
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('Marketing', 'Los Angeles'),
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('Sales', 'Boston'),
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('Operations', 'Houston'),
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('Research', 'Seattle'),
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('Customer Support', 'Austin');
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INSERT INTO job (job_title, min_salary, max_salary) VALUES
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('Manager', 60000.00, 100000.00),
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('Developer', 50000.00, 80000.00),
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('Analyst', 45000.00, 70000.00),
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('Designer', 40000.00, 65000.00),
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('Sales Executive', 35000.00, 60000.00),
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('HR Specialist', 40000.00, 70000.00),
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('Finance Analyst', 50000.00, 75000.00),
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('Marketing Coordinator', 45000.00, 70000.00),
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('Operations Manager', 55000.00, 90000.00),
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('Research Scientist', 60000.00, 95000.00),
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('Customer Support Representative', 35000.00, 55000.00);
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INSERT INTO employee (emp_name, salary, hire_date, dept_id, job_id) VALUES
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('Alice', 70000.00, '2020-01-15', 1, 1),
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('Bob', 65000.00, '2019-03-22', 2, 2),
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('Charlie', 55000.00, '2018-07-30', 2, 3),
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('David', 60000.00, '2021-05-10', 3, 4),
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('Eva', 50000.00, '2017-11-05', 4, 5),
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('Frank', 75000.00, '2016-09-12', 5, 1),
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('Grace', 48000.00, '2022-02-20', 1, 2),
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('Henry', 52000.00, '2021-08-15', 2, 3),
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('Ivy', 58000.00, '2020-04-10', 3, 4),
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('Jack', 62000.00, '2019-12-01', 4, 5),
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('Katie', 53000.00, '2021-07-25', 5, 6),
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('Leo', 67000.00, '2018-05-18', 6, 7),
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('Mona', 49000.00, '2020-11-30', 7, 8),
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('Nina', 71000.00, '2019-02-14', 8, 9),
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('Oscar', 56000.00, '2022-03-05', 1, 10),
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('Paul', 63000.00, '2021-09-12', 2, 11),
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('Quincy', 54000.00, '2020-06-20', 3, 1),
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('Rachel', 59000.00, '2019-08-15', 4, 2),
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('Steve', 68000.00, '2018-12-10', 5, 3),
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('Tina', 51000.00, '2022-01-22', 6, 4),
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('Uma', 72000.00, '2021-04-18', 7, 5),
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('Victor', 57000.00, '2020-07-30', 8, 6),
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('Wendy', 64000.00, '2019-10-05', 1, 7),
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('Xander', 50000.00, '2022-05-12', 2, 8),
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('Yara', 69000.00, '2021-03-25', 3, 9),
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('Zack', 55000.00, '2020-09-15', 4, 10),
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('Amy', 61000.00, '2019-06-20', 5, 11),
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('Brian', 74000.00, '2018-04-10', 6, 1),
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('Cathy', 52000.00, '2022-07-18', 7, 2),
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('Derek', 67000.00, '2021-12-01', 8, 3);
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```
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### `SIGNAL` 语句的基本语法
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```sql
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SIGNAL SQLSTATE '状态码'
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SET MESSAGE_TEXT = '错误消息';
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```
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- **SQLSTATE**：一个 5 字符的字符串，表示错误的状态码。MySQL 使用 `'45000'` 表示用户定义的错误。
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- **MESSAGE_TEXT**：自定义的错误消息，用于描述错误的原因。
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### 练习题
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#### 练习题 1: 工资范围验证
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创建一个触发器 `before_employee_insert`，在插入 `employee` 表数据之前，检查员工的工资是否在其对应职位的 `min_salary` 和 `max_salary` 范围内。如果超出范围，阻止插入并抛出错误。
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```sql
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DELIMITER $$
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DROP TRIGGER IF EXISTS before_employee_insert;
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CREATE TRIGGER before_employee_insert
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BEFORE INSERT ON employee
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FOR EACH ROW
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BEGIN
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IF NEW.salary > (
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SELECT j.max_salary
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FROM job j
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WHERE j.job_id = NEW.job_id
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) OR NEW.salary < (
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SELECT j.min_salary
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FROM job j
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WHERE j.job_id = NEW.job_id
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) THEN
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SIGNAL SQLSTATE '45000'
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SET MESSAGE_TEXT = '工资值错误，不在职务工资范围内';
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END IF;
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END $$
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DELIMITER ;
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INSERT INTO employee
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VALUES(DEFAULT, '雷昊', 0, NOW(), 1, 1);
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```
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#### 练习题 2: 自动更新部门人数
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创建一个触发器 `after_employee_insert`，在插入 `employee` 表数据之后，自动更新 `department` 表中的部门人数（假设 `department` 表新增一个字段 `employee_count`）。
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```sql
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ALTER TABLE department ADD employee_count INT UNSIGNED;
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DELIMITER $$
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DROP TRIGGER IF EXISTS after_employee_insert;
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CREATE TRIGGER after_employee_insert
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AFTER INSERT ON employee
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FOR EACH ROW
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BEGIN
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UPDATE department d
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SET d.employee_count = (
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SELECT COUNT(*)
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FROM employee e
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WHERE e.dept_id = d.dept_id
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);
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END $$
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DELIMITER ;
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INSERT INTO employee
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VALUES(DEFAULT, '雷昊', 60000.00, NOW(), 1, 1);
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```
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#### 练习题 3: 工资变更日志
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创建一个触发器 `after_employee_update`，在更新 `employee` 表的 `salary` 字段后，将变更记录插入到一个新的日志表 `salary_log` 中，记录员工 ID、旧工资、新工资和变更时间。
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```sql
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DROP TABLE IF EXISTS salary_log;
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CREATE TABLE salary_log(
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emp_id INT,
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old_salary DECIMAL(10, 2),
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new_slaray DECIMAL(10, 2),
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update_date DATE
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);
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DELIMITER $$
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DROP TRIGGER IF EXISTS after_employee_update;
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CREATE TRIGGER after_employee_update
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BEFORE UPDATE ON employee
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FOR EACH ROW
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BEGIN
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IF NEW.salary <> OLD.salary THEN
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INSERT INTO salary_log()
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VALUES(NEW.emp_id, OLD.salary, NEW.salary, NOW());
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END IF;
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END $$
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DELIMITER ;
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UPDATE employee e
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SET e.salary = 10
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WHERE e.emp_id = 1;
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```
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#### 练习题 4: 删除员工时备份数据
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创建一个触发器 `before_employee_delete`，在删除 `employee` 表数据之前，将被删除的员工数据插入到一个备份表 `employee_backup` 中。
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```sql
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CREATE TABLE employee_backup AS
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SELECT *
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FROM employee
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WHERE 0;
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DELIMITER $$
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DROP TRIGGER IF EXISTS before_employee_delete;
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CREATE TRIGGER before_employee_delete
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BEFORE DELETE ON employee
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FOR EACH ROW
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BEGIN
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INSERT INTO employee_backup()
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VALUES(OLD.emp_id, OLD.emp_name, OLD.salary, OLD.hire_date, OLD.dept_id, OLD.job_id);
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END $$
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DELIMITER ;
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DELETE FROM employee
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WHERE emp_id = 20;
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```
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#### 练习题 5: 自动设置默认职位
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创建一个触发器 `before_employee_insert`，在插入 `employee` 表数据时，如果未指定 `job_id`，则自动将其设置为 `job` 表中的默认职位（假设默认职位的 `job_id` 为 1）。
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```sql
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DELIMITER $$
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DROP TRIGGER IF EXISTS before_employee_insert;
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CREATE TRIGGER before_employee_insert
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BEFORE INSERT ON employee
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FOR EACH ROW
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BEGIN
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IF NEW.job_id IS NULL THEN
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SET NEW.job_id = 1;
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END IF;
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END $$
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DELIMITER ;
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INSERT INTO employee
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VALUES(DEFAULT, '雷昊', 60000.00, NOW(), 1, NULL);
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```
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#### 练习题 6: 防止修改入职日期
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创建一个触发器 `before_employee_update`，在更新 `employee` 表数据时，防止修改 `hire_date` 字段。如果尝试修改，抛出错误。
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```sql
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DELIMITER $$
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DROP TRIGGER IF EXISTS before_employee_update;
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CREATE TRIGGER before_employee_update
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BEFORE UPDATE ON employee
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FOR EACH ROW
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BEGIN
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IF NEW.hire_date <> OLD.hire_date THEN
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SIGNAL SQLSTATE '45000'
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SET MESSAGE_TEXT='不允许修改用户的入职时间';
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END IF;
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END $$
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DELIMITER ;
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UPDATE employee e
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SET e.hire_date = '2025-3-20'
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WHERE e.emp_id = 1;
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```
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#### 练习题 7: 自动计算工龄
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创建一个触发器 `before_employee_insert`，在插入 `employee` 表数据时，自动计算员工的工龄（以年为单位），并将其存储到一个新字段 `years_of_service` 中。
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```sql
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ALTER TABLE employee ADD years_of_service INT;
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DELIMITER $$
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DROP TRIGGER IF EXISTS before_employee_insert;
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CREATE TRIGGER before_employee_insert
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BEFORE INSERT ON employee
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FOR EACH ROW
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BEGIN
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SET NEW.years_of_service = TIMESTAMPDIFF(YEAR,NEW.hire_date,NOW());
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END $$
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DELIMITER ;
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SELECT TIMESTAMPDIFF(YEAR,e.hire_date,NOW())
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FROM employee e;
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INSERT INTO employee
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VALUES(DEFAULT, '雷昊', 60000.00, '2022-12-31', 1, 1, NULL);
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```
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#### 练习题 8: 防止删除部门
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创建一个触发器 `before_department_delete`，在删除 `department` 表数据之前，检查该部门是否还有员工。如果有员工，阻止删除并抛出错误。
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```sql
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DELIMITER $$
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DROP TRIGGER IF EXISTS before_department_delete;
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CREATE TRIGGER before_department_delete
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BEFORE DELETE ON department
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FOR EACH ROW
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BEGIN
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IF (SELECT COUNT(*) FROM employee e WHERE e.dept_id = OLD.dept_id) > 0 THEN
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SIGNAL SQLSTATE '45000'
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SET MESSAGE_TEXT = '该部门有员工无法删除';
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END IF;
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END $$
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DELIMITER ;
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DELETE FROM department
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WHERE dept_id = 1;
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```
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#### 练习题 9: 自动更新职位工资范围
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创建一个触发器 `after_job_update`，在更新 `job` 表的 `min_salary` 或 `max_salary` 字段后，自动调整 `employee` 表中相关员工的工资，使其符合新的工资范围。
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```sql
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DELIMITER $$
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DROP TRIGGER IF EXISTS after_job_update;
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CREATE TRIGGER after_job_update
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AFTER UPDATE ON job
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FOR EACH ROW
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BEGIN
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UPDATE employee
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SET salary = IF(salary > NEW.max_salary, NEW.max_salary, IF(salary < NEW.min_salary, min_salary, salary))
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WHERE job_id = NEW.job_id;
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END $$
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DELIMITER ;
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```
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#### 练习题 10: 记录部门变更
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创建一个触发器 `after_employee_update`，在更新 `employee` 表的 `dept_id` 字段后，将变更记录插入到一个新的日志表 `department_change_log` 中，记录员工 ID、旧部门 ID、新部门 ID 和变更时间。
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```sql
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CREATE TABLE department_change_log(
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emp_id INT,
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old_dept_id INT,
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new_dept_id INT,
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update_date DATE
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);
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DELIMITER $$
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DROP TRIGGER IF EXISTS after_employee_update;
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CREATE TRIGGER after_employee_update
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AFTER UPDATE ON employee
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FOR EACH ROW
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BEGIN
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IF NEW.dept_id <> OLD.dept_id THEN
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INSERT INTO department_change_log()
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VALUES(NEW.emp_id, OLD.dept_id, NEW.dept_id, NOW());
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END IF;
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END $$
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DELIMITER ;
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```
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#### 练习题 11: 防止插入重复职位
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创建一个触发器 `before_job_insert`，在插入 `job` 表数据之前，检查职位名称是否已存在。如果存在，阻止插入并抛出错误。
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```sql
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DELIMITER $$
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DROP TRIGGER IF EXISTS before_job_insert;
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CREATE TRIGGER before_job_insert
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BEFORE INSERT ON job
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FOR EACH ROW
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BEGIN
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IF (SELECT COUNT(*) FROM job WHERE job_id = NEW.job_id) = 1 THEN
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SIGNAL SQLSTATE '45000'
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SET MESSAGE_TEXT = '职位名称已存在';
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END IF;
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END $$
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DELIMITER ;
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```
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#### 练习题 12: 自动更新员工总数
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创建一个触发器 `after_employee_insert`，在插入 `employee` 表数据之后，自动更新一个统计表 `employee_statistics` 中的员工总数。
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```sql
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CREATE TABLE employee_statistics(
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marking VARCHAR(20),
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num INT
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);
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INSERT INTO employee_statistics()
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VALUES('count', 0);
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DELIMITER $$
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DROP TRIGGER IF EXISTS after_employee_insert;
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CREATE TRIGGER after_employee_insert
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AFTER INSERT ON employee
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FOR EACH ROW
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BEGIN
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UPDATE employee_statistics
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SET num = (SELECT COUNT(*) FROM employee)
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WHERE marking = 'count';
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END $$
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DELIMITER ;
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```
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#### 练习题 13: 防止修改部门所在地
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创建一个触发器 `before_department_update`，在更新 `department` 表数据时，防止修改 `location` 字段。如果尝试修改，抛出错误。
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```sql
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DELIMITER $$
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DROP TRIGGER IF EXISTS before_department_update;
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CREATE TRIGGER before_department_update
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BEFORE UPDATE ON department
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FOR EACH ROW
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BEGIN
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IF NEW.location <> OLD.location THEN
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SIGNAL SQLSTATE '45000'
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SET MESSAGE_TEXT = '无法更新部分的位置';
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END IF;
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END $$
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DELIMITER ;
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```
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#### 练习题 14: 自动调整工资
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创建一个触发器 `before_employee_insert`，在插入 `employee` 表数据时，如果工资低于职位的最低工资，则自动将其调整为最低工资。
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#### 练习题 15: 记录职位变更
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创建一个触发器 `after_employee_update`，在更新 `employee` 表的 `job_id` 字段后，将变更记录插入到一个新的日志表 `job_change_log` 中，记录员工 ID、旧职位 ID、新职位 ID 和变更时间。
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#### 练习题 16: 防止删除职位
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创建一个触发器 `before_job_delete`，在删除 `job` 表数据之前，检查该职位是否还有员工。如果有员工，阻止删除并抛出错误。
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#### 练习题 17: 自动更新部门平均工资
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创建一个触发器 `after_employee_insert`，在插入 `employee` 表数据之后，自动更新 `department` 表中的部门平均工资（假设 `department` 表新增一个字段 `avg_salary`）。
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#### 练习题 18: 防止插入未来入职日期
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创建一个触发器 `before_employee_insert`，在插入 `employee` 表数据时，检查 `hire_date` 是否晚于当前日期。如果是，阻止插入并抛出错误。
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#### 练习题 19: 自动生成员工编号
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创建一个触发器 `before_employee_insert`，在插入 `employee` 表数据时，自动生成一个唯一的员工编号（格式为 `EMP-年份-序号`，例如 `EMP-2023-001`），并将其存储到一个新字段 `emp_code` 中。
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#### 练习题 20: 记录员工离职
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创建一个触发器 `after_employee_delete`，在删除 `employee` 表数据之后，将被删除的员工信息插入到一个离职记录表 `employee_exit_log` 中，记录员工 ID、姓名、离职时间和原因（假设原因由用户输入）。 |