Database connection

[mannel]

Hello everyone,
I'm begining in qt and i want to create connection between a simple qt application with database,but the connection always fails .I did many researchs but i didn't know
where is the problem.
Here is the mainWindow.cpp where i did the connection:

#include <QMainWindow>
#include <QtSql>
#include <QtDebug>
#include <QFileInfo>
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QSqlDatabase mydb=QSqlDatabase::addDatabase("QODBC");
    mydb.setDatabaseName("XE");
    mydb.setUserName("SYS ");
   // mydb.setPort(1521);
    mydb.setPassword("123456");
    if(!mydb.open())
         ui->label->setText("no connexion");
    else
        ui->label->setText("connected ");
}

Dear friends ,I have two big points that I didn't understand :
**1-**What is the difference between QOCI and QODBC and how to know which one i have to use ?
**2-**I saw the qt Documentation where it says:
but I didn't find odbc.pro in sqldrivers directory .So should I install the odbc header and include files?if yes I should ,how can Iinstall them?

I'm student and I need this to work so I will be so glad if you help me to solve the problem
And thanks in advance.

[Moved to General and Desktop ~kshegunov]

[jsulm]

@mannel What is the database you're trying to connect to?
Also do you really have a space in the user name?

mydb.setUserName("SYS ");

[raven-worx]

@mannel
please also note that ODBC interface sometimes also requires the credentials in the connection string (i don't know if it also works via the setter- and getter-methods)

Example for a Microsoft SQL Server accessed via ODBC:

QString connectionString = QString("Driver={SQL Server};Server=%1;Database=%2;Uid=%3;Pwd=%4").arg("127.0.0.1").arg("MyDatabaseName").arg("Username").arg("Password");
db = QSqlDatabase::addDatabase("QODBC");
db.setDatabaseName( connectionString );