PHP で「mysql_」拡張機能を安全に使用して SQL インジェクションを防ぎ、コードの安全性を強化するにはどうすればよいですか?

<?php

// Set HTTP headers for character encoding
header('Content-type: text/html; charset=utf-8');

// Enable error reporting for development and testing
error_reporting(E_ALL | E_STRICT);
ini_set('display_errors', 1);
// In production, set 'display_errors' to 0 to suppress PHP error messages

// Database configuration (modify as needed)
$config = [
    'host' => '127.0.0.1',
    'user' => 'my_user',
    'pass' => 'my_pass',
    'db' => 'my_database'
];

// Connect to the database and disable MySQL error output
$connection = @mysql_connect($config['host'], $config['user'], $config['pass']);
if (!$connection) {
    trigger_error('Unable to connect to database: ' . mysql_error(), E_USER_ERROR);
}

// Select the database
if (!mysql_select_db($config['db'])) {
    trigger_error('Unable to select db: ' . mysql_error(), E_USER_ERROR);
}

// Set character encoding for the connection
if (!mysql_set_charset('utf8')) {
    trigger_error('Unable to set charset for db connection: ' . mysql_error(), E_USER_ERROR);
}

// Accept and sanitize POST values
$id = (int) $_POST['id']; // To prevent SQL injection
$name = mysql_real_escape_string($_POST['name']); // Protects against SQL injection

// Construct and execute the UPDATE query
$result = mysql_query(
    'UPDATE tablename SET name = "' . $name . '" WHERE id = "' . $id . '"'
);

// Check the result and provide feedback
if ($result) {
    echo htmlentities($name, ENT_COMPAT, 'utf-8') . ' updated.';
} else {
    trigger_error('Unable to update db: ' . mysql_error(), E_USER_ERROR);
}
?>