void MainWindow::on_pushButton_clicked()
{
    QString username = ui->text_username->text();
    QString password = ui->text_password->text();

    const QString DRIVER("QSQLITE");

    if(QSqlDatabase::isDriverAvailable(DRIVER))
    {
        QSqlDatabase db = QSqlDatabase::addDatabase(DRIVER);

        db.setDatabaseName("school");

        if(!db.open())
            qWarning() << "MainWindow::DatabaseConnect - ERROR: " << db.lastError().text();
    }
    else
        qWarning() << "MainWindow::DatabaseConnect - ERROR: no driver " << DRIVER << " available";

    QSqlQuery qry;

    if (qry.exec("select * from accounts where username='"+username+"' and password="+password+"'")){
        int count;
        while (qry.next()){
            count++;
        }
        if(count==1){
            //start listwindow.ui
            this->hide();
            listwindow = new ListWindow(this);
            listwindow->show();
        }
        else{
            QMessageBox::warning(this, "Warning", "Password is incorrect");
        }
    }
}