PHP programming tips to prevent SQL injection attacks

PHP Programming Tips to Prevent SQL Injection Attacks

Introduction:
SQL injection is a common way to attack web applications. The attacker inserts malicious SQL code into the data entered by the user, thereby Gain illegal access to the database or perform malicious operations. To protect our applications from SQL injection attacks, we need to adopt some programming techniques to filter, escape, and validate user-entered data. This article will discuss several common PHP programming techniques to help us prevent SQL injection attacks.

1. Use prepared statements
   Prepared statements are a powerful tool in PHP to prevent SQL injection. It ensures that the entered data is properly escaped and treated as data and not part of the SQL code. Here is an example of using prepared statements:

$mysqli = new mysqli("localhost", "username", "password", "database");

if($mysqli->connect_error) {
    die("连接数据库失败: " . $mysqli->connect_error);
}

$stmt = $mysqli->prepare("SELECT * FROM users WHERE username = ? AND password = ?");
$stmt->bind_param("ss", $username, $password);

$username = $_POST['username'];
$password = $_POST['password'];

$stmt->execute();
$result = $stmt->get_result();

while($row = $result->fetch_assoc()) {
    // 处理结果集
}

$stmt->close();

2. Using parameterized queries
   Similar to prepared statements, parameterized queries can also prevent SQL injection attacks. We can use the PDO library to perform parameterized queries. Here is an example of using parameterized queries:

$dsn = 'mysql:host=localhost;dbname=database';
$username = 'username';
$password = 'password';

try {
    $pdo = new PDO($dsn, $username, $password);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $e) {
    die("连接数据库失败：" . $e->getMessage());
}

$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username AND password = :password");
$stmt->bindParam(':username', $username);
$stmt->bindParam(':password', $password);

$username = $_POST['username'];
$password = $_POST['password'];

$stmt->execute();
$result = $stmt->fetchAll(PDO::FETCH_ASSOC);

foreach($result as $row) {
    // 处理结果集
}

$stmt->closeCursor();

3. Input validation and filtering
   In addition to using prepared statements and parameterized queries, we should also validate and filter user input filter. This helps us detect and block malicious input. Here is an example of validating and filtering user input:

$username = $_POST['username'];
$password = $_POST['password'];

if(!empty($username) && !empty($password)) {
    // 验证用户名和密码是否符合要求，如长度、字符等
    // ...
    
    // 过滤特殊字符
    $username = filter_var($username, FILTER_SANITIZE_STRING);
    $password = filter_var($password, FILTER_SANITIZE_STRING);
    
    // 执行SQL查询
    // ...
} else {
    die("用户名和密码不能为空");
}

Summary:
To prevent SQL injection attacks, we must take steps to filter, escape, and validate user-entered data. Using prepared statements and parameterized queries can effectively prevent SQL injection attacks. At the same time, input validation and filtering are also important defensive measures. By using these PHP programming tips, we can improve the security of our applications and protect user information and database security.

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