CREATE TABLE users ( user_id int NOT NULL AUTO_INCREMENT, username varchar(50) NOT NULL, password varchar(50) NOT NULL, phone varchar(50) NOT NULL, PRIMARY KEY (user_id) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4; CREATE TABLE products ( product_id int NOT NULL AUTO_INCREMENT, product_name varchar(50) NOT NULL, product_description varchar(200) NOT NULL, product_price decimal(10,2) NOT NULL, PRIMARY KEY (product_id) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4; CREATE TABLE shopping_cart ( user_id int NOT NULL, product_id int NOT NULL, quantity int NOT NULL, PRIMARY KEY (user_id,product_id), FOREIGN KEY (user_id) REFERENCES users (user_id) ON DELETE CASCADE ON UPDATE CASCADE, FOREIGN KEY (product_id) REFERENCES products (product_id) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4; CREATE TABLE orders ( id INT AUTO_INCREMENT PRIMARY KEY, user_id INT, product_id INT, quantity INT, total DECIMAL(10, 2), order_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP, FOREIGN KEY (user_id) REFERENCES users(user_id), FOREIGN KEY (product_id) REFERENCES products(product_id) ); 实现下订单功能，并在下了订单之后，把商品从购物车里删了 sql语句

以下是实现下订单功能，并在下了订单之后，把商品从购物车里删了的 SQL 语句：

-- 首先插入订单信息到 orders 表中
INSERT INTO orders (user_id, product_id, quantity, total)
SELECT user_id, product_id, quantity, product_price * quantity
FROM shopping_cart
JOIN products ON shopping_cart.product_id = products.product_id
WHERE user_id = [用户ID];

-- 然后删除购物车中对应的商品
DELETE FROM shopping_cart
WHERE user_id = [用户ID] AND product_id = [商品ID];

其中，将 `[用户ID]` 和 `[商品ID]` 替换为实际的用户 ID 和商品 ID 即可。另外，`orders` 表中的 `total` 字段为订单总价，根据购买数量和商品单价计算得出。

相关问题

建表语句是CREATE TABLE users ( id INT(11) NOT NULL AUTO_INCREMENT, username VARCHAR(50) NOT NULL, password VARCHAR(255) NOT NULL, email VARCHAR(100) NOT NULL, created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP, updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, PRIMARY KEY (id), UNIQUE KEY username (username), UNIQUE KEY email (email)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;。你插入的这个语句报错了，请重新写

非常抱歉，我的回答有误。以下是一个可以向上面的users表插入200000条数据的SQL语句，它与之前的SQL语句略有不同：

INSERT INTO users (username, password, email, created_at, updated_at) 
SELECT 
    CONCAT('user', LPAD(n, 6, '0')), 
    MD5(CONCAT('password', LPAD(n, 6, '0'))), 
    CONCAT('user', LPAD(n, 6, '0'), '@example.com'), 
    NOW(), 
    NOW()
FROM 
    (SELECT @row_number:=@row_number+1 AS n FROM 
        (SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4) t1, 
        (SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4) t2, 
        (SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4) t3, 
        (SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4) t4,
        (SELECT @row_number:=0) AS x
    ) numlist
LIMIT 200000;

这个SQL语句使用了一个嵌套的SELECT语句，生成了从1到200000的序列号，然后根据序列号生成了随机的用户名、密码和电子邮件信息，并将这些信息插入到users表中。这个SQL语句也增加了一个LIMIT子句，以限制插入的行数为200000行。

import pymysql# 连接数据库conn = pymysql.connect(host='localhost', port=3306, user='root', password='password', db='user_management', charset='utf8')cursor = conn.cursor()# 创建用户表cursor.execute('CREATE TABLE IF NOT EXISTS users (id INT PRIMARY KEY AUTO_INCREMENT, username VARCHAR(20) NOT NULL, password VARCHAR(20) NOT NULL, permission INT)')# 用户注册def register(username, password): cursor.execute("INSERT INTO users (username, password, permission) VALUES (%s, %s, %s)", (username, password, 1)) conn.commit()# 用户登录def login(username, password): cursor.execute("SELECT * FROM users WHERE username = %s AND password = %s", (username, password)) user = cursor.fetchone() if user: return user[0] else: return None# 修改密码def change_password(user_id, new_password): cursor.execute("UPDATE users SET password = %s WHERE id = %s", (new_password, user_id)) conn.commit()# 关闭数据库连接cursor.close()conn.close()中无法import pymysql

这可能是因为你的Python环境没有安装pymysql库导致的。你可以在命令行中使用以下命令安装：

pip install pymysql

如果仍然出现问题，可以尝试升级pip：

pip install --upgrade pip

如果还是不行，可以尝试使用其他SQL库，比如sqlite3或者MySQL Connector/Python等。