Select from SQL when combo box selection index changed c#

Question

Select from SQL for workers work hours monthly when chose frome combo box

 

string saveStaff = "SELECT  [radnik] as Radnik,SUM(cast((CASE WHEN DATEPART(WEEKDAY, vrijemeprijave) in (1, 7) then 0 else (CASE WHEN(DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) > 8 THEN 8 ELSE(DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) END) end)as float))   AS radni_sati,"
                     + "SUM(cast((CASE WHEN DATEPART(WEEKDAY, vrijemeodjave) in (1, 7) then(DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) else(case when(DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) > 8  then((DATEDIFF(SECOND, vrijemeprijave, vrijemeodjave) / 3600) - 8) ELSE 0 END) end)as float))   AS 'Prekovremeni'"
                     + "from[prijava_radnika]"
                     + "where MONTH([vrijemeprijave]) = MONTH('" + mjeseccomboBox.Text.ToString() + "') "
                     + "group by[radnik]";

 Combo box fill

 

private void punjenje_comboboxa_mjesecgodina()
        {
           mjeseccomboBox.DataSource = CultureInfo.InvariantCulture.DateTimeFormat
                                                     .MonthNames.Take(12).ToList();
            mjeseccomboBox.SelectedItem = CultureInfo.InvariantCulture.DateTimeFormat
                                                    .MonthNames[DateTime.Now.AddMonths(-1).Month - 1];

            godinacomboBox.DataSource = Enumerable.Range(1983, DateTime.Now.Year - 1983 + 1).ToList();
           godinacomboBox.SelectedItem = DateTime.Now.Year;


        }