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 .

[Lykurg]

See QSqlQuery::value().

[hohoanganh205]

Thanks you very much, I done.

QSqlQuery q("select count(MaDaiLy) as SoDaiLyTrongQuan from DaiLy, Quan where DaiLy.Quan_TenQuan = Quan.TenQuan and Quan.TenQuan = '" + ui.cbTenQuan->currentText() + "'");
		QSqlRecord rec = q.record();
		int nameCol = rec.indexOf("SoDaiLyTrongQuan"); // index of the field "name"
		q.next();
		int SoDLHienCoTrongQuan = q.value(nameCol).toInt();

QSqlQuery q("select count(MaDaiLy) as SoDaiLyTrongQuan from DaiLy, Quan where DaiLy.Quan_TenQuan = Quan.TenQuan and Quan.TenQuan = '" + ui.cbTenQuan->currentText() + "'");
		QSqlRecord rec = q.record();
		int nameCol = rec.indexOf("SoDaiLyTrongQuan"); // index of the field "name"
		q.next();
		int SoDLHienCoTrongQuan = q.value(nameCol).toInt();

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the result is return: 2

[Lykurg]

Hi, since you only query one "field" the index is 0. Thus you can simplify your code:

QSqlQuery q("select count(MaDaiLy) from DaiLy, Quan where DaiLy.Quan_TenQuan = Quan.TenQuan and Quan.TenQuan = '" + ui.cbTenQuan->currentText() + "'");
q.next();
int SoDLHienCoTrongQuan = q.value(0).toInt();

QSqlQuery q("select count(MaDaiLy) from DaiLy, Quan where DaiLy.Quan_TenQuan = Quan.TenQuan and Quan.TenQuan = '" + ui.cbTenQuan->currentText() + "'");
q.next();
int SoDLHienCoTrongQuan = q.value(0).toInt();

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Further have a look at QSqlQuery::bindValue().