关于数据库中datareader的用法

1.C#中提供的DataReader可以从数据库中每次提取一条数据。

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

namespace WindowsApplication4
{
    publicpartial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
       
        //定义链接
        OleDbConnection conn;
        //定义命令
        OleDbCommand cmd;
        //定义datareader
        OleDbDataReader myreader;
        //定义两个变量用来存储数据库链接字符串和命令字符串
        string connstr, selectcmd;
        private void button1_Click(object sender, EventArgs e)
        {
            connstr = "Provider=Microsoft.Jet.OLEDB.4.0;DataSource=db.mdb";
            selectcmd = "select * from yonghu where username='" + textBox1.Text+ "' and password='" + textBox2.Text + "'";
            //实例化链接并打开
            conn = new OleDbConnection(connstr);
            conn.Open();
            //实例化cmd并制定执行语句与执行链接
            cmd = new OleDbCommand(selectcmd, conn);
            //执行查询命令并赋给datareader
            myreader = cmd.ExecuteReader();
           
            if (myreader.Read())
            {
                //myreader中有数据，表示给出的用户名和密码在数据库中有匹配记录
                MessageBox.Show("登录成功");
                //如果登录成功则取出用户名和等级填入下面的文本框中
                textBox3.Text = myreader["username"].ToString();
                textBox4.Text = myreader["level"].ToString();
            }
            else
            {
                //myreader中没有数据，表示给出的用户名和密码至少有一个是错的
                MessageBox.Show("登录失败！！");
            }
            myreader.Close();
            conn.Close();
           
        }

private void button2_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }
    }
}

WeatherTest.WeatherWS ss = new WeatherTest.WeatherWS();
DataSet DS = ss.getRegionDataset();
//Response.Write(ss.getRegionDataset());
GridView1.DataSource = DS.Tables[0];
GridView1.DataBind();

转载：http://blog.sina.com.cn/s/blog_4ae95c270101ltnv.html