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

//數據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); //客戶端和數據庫不在同一臺機器，可以使用下面的連接方式 using System.Data.OleDb; //HOST是Oracle數據庫服務器地址，PORT是Oracle數據庫端口，SERVICE_NAME是數據庫名稱 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)   {    //新建一個數據庫連接    using(SqlConnection conn = new SqlConnection(GetConnectString()))    {     conn.Open();//打開數據庫     //Console.WriteLine("數據庫打開成功!");     //創建數據庫命令     SqlCommand cmd = conn.CreateCommand();     //創建查詢語句     cmd.CommandText = "SELECT * FROM userinfo";     //從數據庫中讀取數據流存入reader中     SqlDataReader reader = cmd.ExecuteReader();              //從reader中讀取下一行數據,如果沒有數據,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列的數據以Int32的格式返回      //reader.GetString(int n)這是將第n列的數據以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"));       //格式輸出數據      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();   }   //得到一個數據庫連接字符串   static string GetConnectString()   {    return "Data Source=(local);Initial Catalog=db1;Integrated Security=SSPI;";   }  } } 

DataTable dt;        //假設字段為name, dt已經保存了數據 dt.rows[0]["name"] == System.DBNull.Value; //判斷第一行數據的name字段是否為空 

DataTable dt;    //假設字段為name, dt已經保存了數據 dt.rows[0].IsNull("name"); //判斷第一行數據的name字段是否為空 

DataTable dt;       //假設字段為name, dt已經保存了數據 dt.rows[0]["name"].ToString() == ""; //判斷第一行數據的name字段是否為空