Below example, query.value(1) will got an QVariant(Invalid) value. But it returned a QVariant(Double) value if I run it on win7(Because win7 does not has such upgrade package).

#include <QCoreApplication>
#include <QSqlDatabase>
#include <QSqlQuery>
#include <QDebug>
#include <QSqlError>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");

    QString dsn = QString("DRIVER=%1;SERVER=%2;PORT=%3;DATABASE=%4;UID=%5;PWD=%6")
            .arg("{SQL Server}")
            .arg("127.0.0.1")
            .arg(1433)
            .arg("TestDB")
            .arg("sa")
            .arg("sa");

    db.setHostName("127.0.0.1");
    db.setDatabaseName(dsn);
    db.setUserName("sa");
    db.setPassword("sa");

    if(!db.open()) {
        qDebug()<<db.lastError().text();
    } else {
        qDebug()<<"database open success!";
        QSqlQuery query(db);
        query.exec("select id, my_float from my_table");
        while(query.next()) {
            qDebug()<<query.value(0) << query.value(1);
        }
        return -1;
    }
}