C#中sqlDataRead 的三种方式遍历读取各个字段数值的方法

create table studentname
(
 id int  primary key identity(1,1) not null ,
name nvarchar(500) not null
)
insert into studentname values('long')
insert into studentname values('long')
insert into studentname values('long')
insert into studentname values('long')
insert into studentname values('long')
insert into studentname values('chao')
insert into studentname values('chao')

using System.Data;
 using System.Data.SqlClient;
string constr = "server=localhost;uid=sa;pwd=longshicheng;database=Student";
      SqlConnection conn = new SqlConnection(constr);
      SqlCommand cmd = new SqlCommand("select * from studentname", conn);
      conn.Open();
      SqlDataReader rdr = cmd.ExecuteReader();
      string makestr = "";
      DataTable table = new DataTable();
      table.Load(rdr); //数据表装入 dataReader 。
      string result="";
      for (int i = 0; i < table.Rows.Count; i++) // 遍历行
      {
        for (int j = 0; j < table.Columns.Count; j++) //遍历列
        {
          result += table.Rows[i][j].ToString(); //逐行逐列显示每个单元格的数值。
        }
        result += Environment.NewLine; //一行遍历完成就写入回车。
      }
      txtlab.Text = result;
      /***************************************************************/

string constr = "server=localhost;uid=sa;pwd=longshicheng;database=Student";
      SqlConnection conn = new SqlConnection(constr);
      SqlCommand cmd = new SqlCommand("select * from studentname", conn);
      conn.Open();
      SqlDataReader rdr = cmd.ExecuteReader();
      string makestr = "";
      for (int k = 0; k < rdr.FieldCount; k++) //获取字段名称
      {
        makestr += rdr.GetName(k) + "\t"; //载入字段名称
      }
      makestr += Environment.NewLine; //换行
      makestr = makestr + "---------------------------------------------"+Environment.NewLine;
      while (rdr.Read()) //逐行读取每一笔记录
      {
        for (int t = 0; t < rdr.FieldCount; t++) //逐列读出
        {
          makestr = makestr + rdr[t].ToString() + "\t"; //累加每一行，也就是逐个字段读出对应的数值
        }
        makestr = makestr + Environment.NewLine; //又一行
      }
      txtinfo.Text = makestr;
      rdr.Close(); //关闭
      conn.Close();
    }

string constr = "server=localhost;uid=sa;pwd=longshicheng;database=Student";
      SqlConnection conn = new SqlConnection(constr);
      SqlCommand cmd = new SqlCommand("select * from studentname", conn);
      conn.Open();
      SqlDataReader rdr = cmd.ExecuteReader();
      string makestr = "";
      for (int k = 0; k < rdr.FieldCount; k++) //获取字段名称
      {
        makestr += rdr.GetName(k) + "\t"; //载入字段名称
      }
      makestr += Environment.NewLine; //换行
      makestr = makestr + "---------------------------------------------" + Environment.NewLine;
      while (rdr.Read()) //逐行读取每一笔记录
      {
        makestr = makestr + rdr.GetValue(0) + " \t" + rdr.GetValue(1).ToString() + "\t";
        makestr = makestr + Environment.NewLine;
      }
      txtother.Text = makestr;
      rdr.Close(); //关闭
      conn.Close();