Python 数据库操作SQL基础

CREATE DATABASE mydb;

CREATE TABLE users (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50) NOT NULL,
    age INT NOT NULL,
    email VARCHAR(100)
);

INSERT INTO users (name, age, email) VALUES ('Alice', 30, 'alice@example.com');

SELECT * FROM users; -- 查询所有数据
SELECT * FROM users WHERE age > 25; -- 查询年龄大于 25 的用户
SELECT name, email FROM users; -- 只查询用户名和电子邮件

SELECT * FROM users ORDER BY age DESC; -- 按年龄降序排序
SELECT age, COUNT(*) FROM users GROUP BY age; -- 按年龄分组，统计每个年龄段的用户数量
SELECT AVG(age) FROM users; -- 计算平均年龄

UPDATE users SET age = 31 WHERE name = 'Alice'; -- 将名为 Alice 的用户年龄更新为 31

DELETE FROM users WHERE id = 1; -- 删除 id 为 1 的用户

CREATE INDEX idx_users_email ON users (email); -- 为 email 列创建索引

-- 假设有另一个表 orders，包含 user_id 和 order_date 列
SELECT users.name, orders.order_date
FROM users
INNER JOIN orders ON users.id = orders.user_id;

SELECT * FROM users WHERE age > (SELECT AVG(age) FROM users); -- 查询年龄大于平均年龄的用户

pip install mysql-connector-python

import mysql.connector
# 连接数据库
cnx = mysql.connector.connect(
    host='localhost',
    user='your_username',
    password='your_password',
    database='mydb'
)
# 创建游标
cursor = cnx.cursor()
# 执行 SQL 语句
cursor.execute('SELECT * FROM users')
# 获取查询结果
result = cursor.fetchall()
for row in result:
    print(row)
# 关闭游标和连接
cursor.close()
cnx.close()