DataReader必须持续连接，所以在调用方法SqlDataReader作为返回类型时候，必须在方法外关闭流，很不方便。

DataAdapter用于对数据源检索数据并填充到DataSet中的表。DataAdapter还可以将DataSet所做的更改进行解析回数据源。

（通俗点，DataSet就是一个缓冲区，可以修改好数据，让DataAdapter返回回数据源）

DataAdapter使用例程

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace DataAdapter
{
    public partial class Form1 : Form
    {
        string constr = "server=QT-201303030913;database=ThreeDb;uid=sa;pwd=daxiang";
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //Bind();
        }

        private void Bind()
        {
            
            string sql = "select * from product";
            SqlDataAdapter sda = new SqlDataAdapter(sql, constr);
            DataSet ds = new DataSet();
            sda.Fill(ds);

            dataGridView1.DataSource = ds.Tables[0];
        }

        private void button1_Click(object sender, EventArgs e)
        {
            using (SqlConnection conn = new SqlConnection(constr))
            {
                SqlCommand cmd = new SqlCommand("select * from product", conn);
                SqlDataAdapter sda = new SqlDataAdapter(cmd);

                DataSet ds = new DataSet();

                sda.Fill(ds,"product");

                dataGridView1.DataSource = ds.Tables["product"];
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            SqlDataAdapter sda = new SqlDataAdapter("select * from product", constr);
            DataSet ds = new DataSet();
            sda.Fill(ds,"p");

            dataGridView1.DataSource = ds.Tables["p"];
        }

        private void button3_Click(object sender, EventArgs e)
        {
            SqlDataAdapter sda = new SqlDataAdapter("select * from product", constr);
            DataSet ds = new DataSet();
            sda.Fill(ds, "p");
            dataGridView1.DataSource = ds.Tables["p"];

            sda.SelectCommand.CommandText = "select * from classify";
            sda.Fill(ds,"c");
            dataGridView2.DataSource = ds.Tables["c"];
        }

        private void dataGridView1_CellClick(object sender, DataGridViewCellEventArgs e)
        {
            string concell = dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Value.ToString();
            string msg = string.Format("您单击的是第{0}行的第{1}列\n当前单元格的内容为\"{2}\"",e.RowIndex.ToString(),e.ColumnIndex.ToString(),concell);
            MessageBox.Show(msg);
        }

    }
}

form1设计

在一个DataSet中多张表名存在大小写，则搜索表名倍认为存在大小写，否则补区分大小写。