string connStr = @"Data Source=D:\database.mdb; Provider=Microsoft.Jet.OleDb.4.0;"; //數(shù)據(jù)庫連接字符串 
OleDbConnection conn = new OleDbConnection(connStr); 

//數(shù)據(jù)庫和客戶端在同一臺機器上 
using System.Data.OracleClient; 
string connStr = "data source=orcl;user=user;password=pwd;"; 
OracleConnection conn = new OracleConnection(connStr); 
//客戶端和數(shù)據(jù)庫不在同一臺機器，可以使用下面的連接方式 
using System.Data.OleDb; 
//HOST是Oracle數(shù)據(jù)庫服務器地址，PORT是Oracle數(shù)據(jù)庫端口，SERVICE_NAME是數(shù)據(jù)庫名稱 
string connStr = "Provider=OraOLEDB.Oracle.1;Data Source=(DESCRIPTION =(ADDRESS_LIST =(ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521)))(CONNECT_DATA =(SERVICE_NAME = orcl)));User ID=message;Password=message;"; 
OleDbConnection conn = new OleDbConnection(connStr); 

using System.Data.SqlClient; 
string connStr = "data source=127.0.0.1;initial catalog=database;user id=sa;pwd=sa"; 
SqlConnection conn = new SqlConnection(connStr); 

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Data.SqlClient; 
 
namespace Login 
{ 
 class Program 
 { 
  static void Main(string[] args) 
  { 
   //新建一個數(shù)據(jù)庫連接 
   using(SqlConnection conn = new SqlConnection(GetConnectString())) 
   { 
    conn.Open();//打開數(shù)據(jù)庫 
    //Console.WriteLine("數(shù)據(jù)庫打開成功!"); 
    //創(chuàng)建數(shù)據(jù)庫命令 
    SqlCommand cmd = conn.CreateCommand(); 
    //創(chuàng)建查詢語句 
    cmd.CommandText = "SELECT * FROM userinfo"; 
    //從數(shù)據(jù)庫中讀取數(shù)據(jù)流存入reader中 
    SqlDataReader reader = cmd.ExecuteReader();     
     
    //從reader中讀取下一行數(shù)據(jù),如果沒有數(shù)據(jù),reader.Read()返回flase 
    while (reader.Read()) 
    { 
     //reader.GetOrdinal("id")是得到ID所在列的index, 
     //reader.GetInt32(int n)這是將第n列的數(shù)據(jù)以Int32的格式返回 
     //reader.GetString(int n)這是將第n列的數(shù)據(jù)以string 格式返回 
     int id = reader.GetInt32(reader.GetOrdinal("id")); 
     string name = reader.GetString(reader.GetOrdinal("name")); 
     string pwd = reader.GetString(reader.GetOrdinal("password")); 
     int age = reader.GetInt32(reader.GetOrdinal("age")); 
     string sex = reader.GetString(reader.GetOrdinal("sex")); 
     string phone = reader.GetString(reader.GetOrdinal("phone")); 
     string address = reader.GetString(reader.GetOrdinal("Address")); 
 
     //格式輸出數(shù)據(jù) 
     Console.Write("ID:{0},Name:{1},PWD:{2},Age:{3},Sex:{4},Phone{5},Address:{6}\n", id, name, pwd, age, sex, phone, address); 
    } 
   } 
   Console.ReadKey(); 
  } 
  //得到一個數(shù)據(jù)庫連接字符串 
  static string GetConnectString() 
  { 
   return "Data Source=(local);Initial Catalog=db1;Integrated Security=SSPI;"; 
  } 
 } 
} 

DataTable dt;        //假設(shè)字段為name, dt已經(jīng)保存了數(shù)據(jù) 
dt.rows[0]["name"] == System.DBNull.Value; //判斷第一行數(shù)據(jù)的name字段是否為空 

DataTable dt;    //假設(shè)字段為name, dt已經(jīng)保存了數(shù)據(jù) 
dt.rows[0].IsNull("name"); //判斷第一行數(shù)據(jù)的name字段是否為空 

DataTable dt;       //假設(shè)字段為name, dt已經(jīng)保存了數(shù)據(jù) 
dt.rows[0]["name"].ToString() == ""; //判斷第一行數(shù)據(jù)的name字段是否為空