What is SQL injection, and how to prevent it?

SQL injection is a malicious attack in which an attacker exploits vulnerabilities in a web application’s input validation to inject malicious SQL code into the application’s database query. This can lead to unauthorized access, data theft, data manipulation, or even the complete compromise of a database. Preventing SQL injection is crucial for maintaining the security and integrity of your PHP-based web applications. Here’s how to prevent SQL injection in PHP:


  1. Prepared Statements:

   – The most effective way to prevent SQL injection is by using prepared statements. These statements separate SQL code from user input, making it impossible for attackers to inject malicious SQL. In PHP, you can use the MySQLi or PDO extension to create prepared statements.

$stmt = $conn->prepare("SELECT * FROM users WHERE username = ?");
$stmt->bind_param("s", $user_input);


  1. Parameterized Queries:

   – If you’re using PDO, you can use parameterized queries, which automatically handle input sanitization and escaping:

$stmt = $conn->prepare("SELECT * FROM users WHERE username = :username");
$stmt->bindParam(':username', $user_input, PDO::PARAM_STR);


  1. Input Validation:

   – Always validate user input to ensure it adheres to expected formats (e.g., emails, numbers) before using it in SQL queries. Use functions like `filter_var()` and custom validation logic.


  1. Escaping Data:

   – If you must include user input directly in SQL queries (not recommended), use proper escaping functions like `mysqli_real_escape_string()` or `PDO::quote()` to escape user input.


  1. Least Privilege Principle:

   – Limit database user privileges to only what is necessary for the application. Avoid using a superuser with full access rights.


  1. Error Handling:

   – Implement robust error handling to log and monitor any unexpected behavior or database errors.


By following these practices, you can significantly reduce the risk of SQL injection in your PHP applications and enhance their security. Prepared statements are the recommended approach, as they offer the most robust protection against this common security threat.

Previously at
Flag Argentina
time icon
Full Stack Engineer with extensive experience in PHP development. Over 11 years of experience working with PHP, creating innovative solutions for various web applications and platforms.