using System.Data; // Use ADO.NET namespace
using System.Data.SqlClient;

SqlConnection thisConnection = new SqlConnection(
@"Data Source=GY; Initial Catalog=northwind;uid=sa;password=datadog"); //先建立连接
thisConnection.Open();//打开连接
SqlCommand thisCommand = thisConnection.CreateCommand();//直接指定conn的command
也可以这样 // SqlCommand cmd = new SqlCommand();
// cmd.Connection = thisConnection;
cmmand的sql命令
thisCommand.CommandText = "SELECT CustomerID, CompanyName from Customer";
SqlDataReader thisReader = thisCommand.ExecuteReader();//sqldatareader不可以用new 必须直接与command关联
//用reader读出表
while (thisReader.Read())
{
// Output ID and name columns
Console.WriteLine("\t{0}\t{1}",
thisReader["CustomerID"], thisReader["CompanyName"]);
// Close reader 用完要关闭
thisReader.Close();