Почему при одном обращении записывается сразу две записи?

Question

[Евгений Павлов]

PHP

class Database {
    private $link;

    public function __construct()
    {
        $this->connect();
    }
    private function connect() {
        $config = require_once 'config/config.php';
        $dsn = 'mysql:host='. $config['host'].';dbname='.$config['db_name'].';charset=' . $config['charset'];
        $this->link = new PDO($dsn, $config['user_name'], $config['password']);

        return $this;
    }
    public function execute($sql) {
        $sth = $this->link->prepare($sql);
        return $sth->execute();
    }
    public function query($sql) {
        $exe = $this->execute($sql);
        print_r($exe);
        $result = $exe->fetchAll(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
        if ($result === false) {
            return [];
        }
        return $result;
    }

}
$db = new Database();
$db->execute('INSERT INTO `user` SET `username`=\'Alex\',`password`=\'222222\', `date`=\'111\'' );