using System.Data;
using System.Data.OleDb;
//......

string strConnection="Provider=Microsoft.Jet.OleDb.4.0;";
strConnection+=@"Data Source=C:\BegASPNET\Northwind.mdb";
OleDbConnection objConnection=new OleDbConnection(strConnection);
//......

objConnection.Open();
objConnection.Close();

using System.Data;
using System.Data.SqlClient;
//...

string strConnection="user id=sa;password=;";
strConnection+="initial catalog=Northwind;Server=YourSQLServer;";
strConnection+="Connect Timeout=30";
SqlConnection objConnection=new SqlConnection(strConnection);
//...

objConnection.Open();
objConnection.Close();

using System.Data.OracleClient;
using System.Data;
private void Button1_Click(object sender, System.EventArgs e)
{
string ConnectionString = "Data Source=sky;user=system;password=manager;";//写连接串
    OracleConnection conn = new oracleConnection(ConnectionString);//创建一个新连接
    try
{
conn.Open();
OracleCommand cmd = conn.CreateCommand();
cmd.CommandText = "select * from MyTable";//在这儿写sql语句
        OracleDataReader odr = cmd.ExecuteReader();//创建一个OracleDateReader对象
        while (odr.Read())//读取数据，如果odr.Read()返回为false的话，就说明到记录集的尾部了
        {
Response.Write(odr.GetOracleString(1).ToString());//输出字段1，这个数是字段索引，具体怎么使用字段名还有待研究
        }
odr.Close();
}
catch (Exception ee)
{
Response.Write(ee.Message); //如果有错误，输出错误信息
    }
finally
{
conn.Close(); //关闭连接
    }
}

using MySQLDriverCS;
// 建立数据库连接
MySQLConnection DBConn;
DBConn = new MySQLConnection(new MySQLConnectionString("localhost", "mysql", "root", "", 3306).AsString);
DBConn.Open();
// 执行查询语句
MySQLCommand DBComm;
DBComm = new MySQLCommand("select Host,User from user", DBConn);
// 读取数据
MySQLDataReader DBReader = DBComm.ExecuteReaderEx();
// 显示数据
try
{
while (DBReader.Read())
{
Console.WriteLine("Host = {0} and User = {1}", DBReader.GetString(0), DBReader.GetString(1));
}
}
finally
{
DBReader.Close();
DBConn.Close();
}
//关闭数据库连接
DBConn.Close();

OleDbConnection1.Open();
//打开数据库连接
OleDbDataAdapter1.Fill(dataSet1, "Address");
//将得来的数据填入dataSet
DataGrid1.DataBind();
//绑定数据
OleDbConnection1.Close();
//关闭连接

//增加数据库数据
//在Web Form上新增对应字段数量个数的TextBox，及一个button，为该按键增加Click响应事件代码如下：

this.OleDbInsertCommand1.CommandText = "InsertsintosADDRESS(NAME,EMAIL, AGE, ADDRESS) VALUES('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "','" + TextBox4.Text + "')";
OleDbInsertCommand1.Connection.Open();
//打开连接
OleDbInsertCommand1.ExecuteNonQuery();
//执行该SQL语句
OleDbInsertCommand1.Connection.Close();
//关闭连接