Avoiding SQL injection in PHP can be done by: 1. Use parameterized queries, as shown in the PDO example. 2. Automatically handle SQL injection using ORM libraries such as Doctrine or Eloquent. 3. Verify and filter user input to prevent other attack types.

How to avoid SQL injection in PHP? This question involves best practices for database security and code writing. SQL injection is a common security vulnerability. By constructing malicious SQL statements, attackers can access or modify data in the database, and even gain control of the database.

To avoid SQL injection, we need to understand its principles and preventive measures. SQL injection is usually done by splicing user input directly into SQL queries, resulting in the query statement being modified or unexpected operations being performed. To give a simple example, if we have a login form, the user name and password entered by the user are spliced ??directly into the SQL query, the attacker can enter ' OR '1'='1 , thereby bypassing authentication.

Let's dive into how to effectively prevent SQL injection in PHP:

First, we need to use parameterized queries (Prepared Statements). This method can separate user input from SQL commands, thus preventing malicious code injection. Here is an example of implementing parameterized query using PDO (PHP Data Objects):

 <?php
$dsn = &#39;mysql:host=localhost;dbname=example&#39;;
$username = &#39;your_username&#39;;
$password = &#39;your_password&#39;;

try {
    $pdo = new PDO($dsn, $username, $password);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
    echo &#39;Connection failed: &#39; . $e->getMessage();
    exit();
}

$username = &#39;john_doe&#39;;
$password = &#39;secret&#39;;

$stmt = $pdo->prepare(&#39;SELECT * FROM users WHERE username = :username AND password = :password&#39;);
$stmt->execute([&#39;username&#39; => $username, &#39;password&#39; => $password]);

$user = $stmt->fetch();

if ($user) {
    echo &#39;Login successful!&#39;;
} else {
    echo &#39;Invalid credentials.&#39;;
}
?>

In this example, we use PDO's prepare method to create a preprocessing statement and pass user input by naming parameters :username and :password . In this way, PDO will automatically process these parameters to prevent SQL injection.

In addition to parameterized queries, we can also use ORM (Object Relational Mapping) libraries such as Doctrine or Eloquent. These libraries usually deal with SQL injection issues automatically, simplifying the development process. For example, use Eloquent's query:

 <?php
use App\Models\User;

$user = User::where(&#39;username&#39;, $username)
            ->where(&#39;password&#39;, $password)
            ->first();

if ($user) {
    echo &#39;Login successful!&#39;;
} else {
    echo &#39;Invalid credentials.&#39;;
}
?>

The ORM library will automatically convert queries into secure SQL statements, avoiding the risk of manually splicing SQL.

In practical applications, some other details need to be paid attention to, such as verifying and filtering user input. While parameterized queries and ORM libraries can effectively prevent SQL injection, verifying user input is still necessary to prevent other types of attacks such as XSS (cross-site scripting attacks).

Regarding performance optimization, using parameterized queries usually does not have a significant impact on performance, but it should be noted that frequent database connections and queries may affect performance. Therefore, it is recommended to use connection pooling and caching mechanisms to optimize database operations.

Finally, share a small experience: developing the habit of using security tools and code audits during development can help identify and fix potential security vulnerabilities early. I once used an automated security scan tool in a project and found some potential SQL injection risks, which made me realize that even if I used parameterized queries, I couldn't take it lightly.

In short, avoiding SQL injection requires starting from multiple aspects. Using parameterized queries and ORM libraries is an effective preventive measure, but it also needs to be combined with other security practices, such as input verification and code auditing, to ensure the security of the application.

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