A simple example using finalize().
// Open the database connection
$db = new SQLite3('database.db');
// Prepare a query for execution
$query = $db->prepare('SELECT user_id FROM users WHERE username=:username');
$query->bindValue(':username', $_COOKIE['username'], SQLITE3_TEXT);
// Execute the query
$result = $query->execute();
// Store the result of the query
$id = $result->fetchArray(SQLITE3_NUM)[0];
// Close the result set and database connection
$result->finalize();
$db->close();
Of course you should be more careful and clean your cookie, etc.