防止sql注入的方法有哪几种

import pymysql

# 建立数据库连接
conn = pymysql.connect(host='localhost', user='root', password='123456', db='mydb')

# 创建游标对象
cursor = conn.cursor()

# 执行参数化查询
username = input("请输入用户名：")
password = input("请输入密码：")
sql = "SELECT * FROM user WHERE username = %s AND password = %s"
cursor.execute(sql, (username, password))

# 获取查询结果
result = cursor.fetchall()

# 处理查询结果
if result:
    print("登录成功！")
else:
    print("用户名或密码错误！")

# 关闭游标和数据库连接
cursor.close()
conn.close()

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

# 建立数据库连接
engine = create_engine('mysql+pymysql://root:123456@localhost/mydb')
Session = sessionmaker(bind=engine)
session = Session()

# 执行查询
username = input("请输入用户名：")
password = input("请输入密码：")
result = session.query(User).filter_by(username=username, password=password).first()

# 处理查询结果
if result:
    print("登录成功！")
else:
    print("用户名或密码错误！")

# 关闭数据库连接
session.close()

<?php
$username = $_POST['username'];
$password = $_POST['password'];

// 验证输入的数据
if (!preg_match("/^[a-zA-Z0-9]{6,}$/", $username)) {
    die("用户名不合法！");
}

// 过滤特殊字符
$username = addslashes($username);
$password = addslashes($password);

// 执行查询
$sql = "SELECT * FROM user WHERE username = '$username' AND password = '$password'";
$result = mysqli_query($conn, $sql);

// 处理查询结果
if (mysqli_num_rows($result) > 0) {
    echo "登录成功！";
} else {
    echo "用户名或密码错误！";
}

// 关闭数据库连接
mysqli_close($conn);
?>