setText not working

[MarkoSan]

What is wrong with this code:

void CCustomerUpdateDialog::slotZipcodeChanged(int iIndex)
{   
    QSqlQuery retrieveCityNameQuery("SELECT * FROM kraj k WHERE k.POSTNA_STEVILKA="+m_pZipcode->currentText());
    QSqlError error=retrieveCityNameQuery.lastError();
    if(error.type()!=QSqlError::NoError)
    {
        qDebug() << retrieveCityNameQuery.lastError();
    } else
    {
        m_pCity->setText(retrieveCityNameQuery.value(1).toString());
    }
};

void CCustomerUpdateDialog::slotZipcodeChanged(int iIndex)
{   
    QSqlQuery retrieveCityNameQuery("SELECT * FROM kraj k WHERE k.POSTNA_STEVILKA="+m_pZipcode->currentText());
    QSqlError error=retrieveCityNameQuery.lastError();
    if(error.type()!=QSqlError::NoError)
    {
        qDebug() << retrieveCityNameQuery.lastError();
    } else
    {
        m_pCity->setText(retrieveCityNameQuery.value(1).toString());
    }
};

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I select a zip code of an city and in the QLineEdit should provide then after click the name of city with selected Zip Code. But, sql i generated ok (double check), QLineEdity still stays empty! Why?