关于switch的一个问题

 string str3 = "select * from xinxi where id='" + id + "'";
            SqlCommand cmd3 = new SqlCommand(str3, conn);
            SqlDataReader sdr3 = cmd3.ExecuteReader();
            if (sdr3.Read())
            {
                string j = sdr3.GetString(7);
                ......
　　　　　　｝
            switch (j)
                                    { 
                                        case "普通员工":
                                            a = a + 500;
                                            break;
                                        case "区域代表":
                                            a = a + 1000;
                                            break;
                                        case "业务总监":
                                            a = a + 1500;
                                            break;
                                        case "经理":
                                            a = a + 2000;
                                            break;
                                    }switch语没有执行  a值没变化请高手解答