C# 连接数据库 中的一些细节（DataSet）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Threading;

namespace CAlianxi2
{
class Program
{
static string connectionstring = "Data Source=.;Initial Catalog=student;User ID=sa;PassWord=shenbao";
static void Main(string[] args)
{
using (SqlConnection conn = new SqlConnection())
{
try
{
conn.ConnectionString = connectionstring;
conn.Open();
SqlCommand cmd = new SqlCommand();
cmd.Connection = conn;
cmd.CommandText = "select *from student";
cmd.CommandType = CommandType.Text;
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds, "student");
Console.WriteLine("student表填充成功");
DisplayResult(ds.Tables["student"]);
cmd.CommandText = "select *from score";

da = new SqlDataAdapter(cmd);
da.Fill(ds, "Score");
Console.WriteLine("Score表填充成功");
DisplayResult(ds.Tables["Score"]);
Console.WriteLine("最后一个是DisplayResult1输出的数据");
DisplayResult1(ds);
Thread.Sleep(10000);
}
catch (SqlException ex)
{
Console.WriteLine("出现错误：{0}", ex.Message);
}
finally
{
if (conn.State == ConnectionState.Open)
{
conn.Close();
}
}
}
}
static void DisplayResult(DataTable dt)
{
SqlConnection connn=new SqlConnection(connectionstring);
connn.Open();
SqlCommand cmd = new SqlCommand("select *from score");
cmd.Connection = connn;
cmd.CommandType = CommandType.Text;
SqlDataReader dR = cmd.ExecuteReader();
Console.WriteLine("这是DisplayResult中读取的数据");
while (dR.Read())
{
Console.WriteLine("{0}{1}{2}", dR[0], dR[1], dR[2]);
}
connn.Dispose();
for (int i = 0; i < dt.Columns.Count; i++)
{
Console.Write(dt.Columns[i].ColumnName.PadRight(10));
}
Console.WriteLine();
for (int i = 0; i < dt.Rows.Count; i++)
{
foreach (DataColumn d in dt.Columns)
{
Console.Write(dt.Rows[i][d].ToString().PadRight(10));
}
Console.WriteLine();
}
}
static void DisplayResult1(DataSet ds)
{
using (DataTableReader dtr = ds.CreateDataReader())
{
while (dtr.Read())
{
Console.WriteLine("{0}{1}{2}", dtr[0], dtr[1], dtr[2]);
}
}
}
}
}