What are common pitfalls to avoid when creating forms in PHP?

One common pitfall to avoid when creating forms in PHP is not properly sanitizing user input, which can leave your application vulnerable to security risks such as SQL injection attacks. To solve this issue, always use functions like htmlspecialchars() or mysqli_real_escape_string() to sanitize user input before using it in your database queries.

// Sanitize user input before using it in a SQL query
$user_input = $_POST['user_input'];
$clean_input = mysqli_real_escape_string($connection, $user_input);
$query = "SELECT * FROM users WHERE username = '$clean_input'";
$result = mysqli_query($connection, $query);