数据库数据输出到excel

             SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=ArchiveSys;Integrated Security=True");
            //SQLHelper sqlhelper = new SQLHelper();
            string sql = "select * from StuFeedback";
            using (SqlCommand cmd = new SqlCommand(sql, conn))
            {
                if (conn.State==ConnectionState.Closed)
                {
                    conn.Open();
                }
                using (SqlDataReader read = cmd.ExecuteReader())
                {
                    if (read.HasRows)
                    {
                        IWorkbook wk = new HSSFWorkbook();//创建workbook
                        ISheet sheet = wk.CreateSheet("stufeedback");//创建工作表
                        int rowIndex = 0;
                        #region 循环创建行与列
                        while (read.Read())
                        {
                            int id = read.GetInt32(0);
                            int? stuid = read.IsDBNull(1) ? null : (int?)read.GetInt32(1);//int?为可控值类型
                            string subtime = read.IsDBNull(2) ? "NULL" : read.GetString(2);
                            int? appstate = read.IsDBNull(3) ? null : (int?)read.GetInt32(3);
                            string stuname = read.IsDBNull(4) ? "NULL" : read.GetString(4);
                            //创建行
                            IRow row = sheet.CreateRow(rowIndex);
                            //创建单元格
                            row.CreateCell(0).SetCellValue(id);
                            #region 若为空值，创建空单元格
                            if (stuid == null)
                            {
                                row.CreateCell(1, CellType.BLANK);
                            }
                            else
                            {
                                row.CreateCell(1).SetCellValue((int)stuid);
                            }
                            #endregion
                            row.CreateCell(2).SetCellValue(subtime);
                            #region 对于空值处理
                            if (appstate == null)
                            {
                                row.CreateCell(3, CellType.BLANK);
                            }
                            else
                            {
                                row.CreateCell(3).SetCellValue((int)appstate);
                            }
                            #endregion
                            row.CreateCell(4).SetCellValue(stuname);
                            rowIndex++;
                        }
                        #endregion
                        using (FileStream fs = File.OpenWrite(@"D:学籍管理stufeedback.xls"))
                        {
                            wk.Write(fs);
                            Response.Write("<script>alert('成功！')</script>");
                        }
                    }
                    else
                    {
                        Response.Write("<script>alert('数据为空！')</script>");
                    }
                }
            }