mysql的not in用法

SELECT column_name(s)
FROM table_name
WHERE column_name NOT IN (subquery);

SELECT *
FROM employees
WHERE department_id NOT IN (SELECT department_id FROM departments);

SELECT *
FROM employees e
WHERE NOT EXISTS (SELECT 1 FROM departments d WHERE d.department_id = e.department_id);

-- 创建示例表
CREATE TABLE users (
    user_id INT PRIMARY KEY,
    username VARCHAR(50)
);

CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    user_id INT,
    order_date DATE
);

-- 插入示例数据
INSERT INTO users (user_id, username) VALUES (1, 'Alice'), (2, 'Bob'), (3, 'Charlie');
INSERT INTO orders (order_id, user_id, order_date) VALUES (1, 1, '2023-01-01'), (2, 2, '2023-01-02');

-- 查询没有订单的用户
SELECT *
FROM users
WHERE user_id NOT IN (SELECT user_id FROM orders);