How can PHP developers prevent form data from being resubmitted and avoid duplicate entries in the database?

To prevent form data from being resubmitted and avoid duplicate entries in the database, PHP developers can use a technique called Post/Redirect/Get (PRG). This involves processing the form data, saving it to the database, and then redirecting the user to another page using the header() function to prevent the form from being resubmitted when the user refreshes the page.

// Process form data
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Save data to the database
    // Redirect to a different page
    header("Location: success.php");
    exit;
}