qt5从mysql数据库中选择数据

我想建立一个登录系统,我有一个MySQL数据库,我想根据我的MySQL数据库用户名和密码登录,但它不起作用。我想我的代码有问题。请检查代码。

void MainWindow::on_loginBtn_clicked()
{

    QSqlDatabase db;

    db = QSqlDatabase::addDatabase("QMYSQL", "MyConnect");
    db.setHostName("localhost");
    db.setUserName("root");
    db.setPassword("");
    db.setDatabaseName("qtregister");

    QString username = ui->loginEdit->text();
    QString password = ui->loginPassword->text();


    if(db.open()) {

        QSqlQuery query(QSqlDatabase::database("MyConnect"));

        query.prepare(QString("SELECT username and password from users where username = :username AND password = :password"));
        query.bindValue(":username", username);
        query.bindValue(":password", password);

        if(!query.exec()) {
            QMessageBox::information(this, "Failed", "Failed To Login");

        }else {
          QMessageBox::information(this, "Success", "Login Success");
        }
    }
    else {
        QMessageBox::information(this, "Not Connected", "Not Conneced Success");
    }
}