How to get value from a query statement ?

[hohoanganh205]

I exec a statement SQL in MYSQL Workbench and result is: 2 ; pic:

2.jpg

But in C++ QT I do not know how to get the value like MYSQL, I try this code and result not is: 2

void QuanLyDaiLy::on_pushButton_clicked()
{
	QSqlQuery *qry = new QSqlQuery();
	qry->prepare("select count(MaDaiLy) as SoDaiLyTrongQuan from DaiLy, Quan where DaiLy.Quan_TenQuan = Quan.TenQuan and Quan.TenQuan = 'Quan 10'");
	qry->exec();
 
	QMessageBox::information(this,"result",QString::number(qry->size()));
}

void QuanLyDaiLy::on_pushButton_clicked()
{
	QSqlQuery *qry = new QSqlQuery();
	qry->prepare("select count(MaDaiLy) as SoDaiLyTrongQuan from DaiLy, Quan where DaiLy.Quan_TenQuan = Quan.TenQuan and Quan.TenQuan = 'Quan 10'");
	qry->exec();

	QMessageBox::information(this,"result",QString::number(qry->size()));
}

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1.png

what can I use to QString::number(qry->????????) to get the value ?

Thanks for help .