PHP と MySQL を使用して Web サイトへのユニーク訪問者を追跡するにはどうすればよいですか?

<?php
// Open database connection
$conn = new mysqli('localhost', 'root', 'password', 'database');

// Get user's IP address
$ip = $_SERVER['REMOTE_ADDR'];

// Check if user already visited today (or in the last week)
$sql = "SELECT * FROM visitors WHERE ip='$ip' AND last_visit >= DATE_SUB(NOW(), INTERVAL 1 DAY)";
$result = $conn->query($sql);

// If user is a new visitor
if ($result->num_rows == 0) {
    // Insert user's IP and current timestamp
    $sql = "INSERT INTO visitors (ip, last_visit) VALUES ('$ip', NOW())";
    $conn->query($sql);

    // Increment total visitor count
    $sql = "UPDATE stats SET visits = visits + 1";
    $conn->query($sql);
}

// Get total number of unique visitors
$sql = "SELECT COUNT(*) AS total_visitors FROM visitors";
$result = $conn->query($sql);
$total_visitors = $result->fetch_assoc()['total_visitors'];

// Display the number of unique visitors
echo "Total unique visitors: $total_visitors";

// Close database connection
$conn->close();
?>