using System;
using System.Data;
using System.Data.OleDb;
using System.Windows.Forms;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string connetionString = null;
            OleDbConnection connection ;
            OleDbDataAdapter oledbAdapter ;
            DataSet ds1 = new DataSet();
            DataSet ds2 = new DataSet();
            DataTable dt ;
            string firstSql = null;
            string secondSql = null;
            int i = 0;
            connetionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Your mdb filename;";
            firstSql = "Your First SQL Statement Here";
            secondSql = "Your Second SQL Statement Here";
            connection = new OleDbConnection(connetionString);
            try
            {
                connection.Open();
                oledbAdapter = new OleDbDataAdapter(firstSql, connection);
                oledbAdapter.Fill(ds1, "First Table");
                oledbAdapter.SelectCommand.CommandText = secondSql;
                oledbAdapter.Fill(ds2, "Second Table");
                oledbAdapter.Dispose();
                connection.Close();

                ds1.Tables[0].Merge(ds2.Tables[0]);
                dt = ds1.Tables[0];

                for (i = 0; i <= dt.Rows.Count - 1; i++)
                {
                    MessageBox.Show(dt.Rows[i].ItemArray[0] + " -- " + dt.Rows[i].ItemArray[0]);

                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("Can not open connection ! ");
            }
        }
    }
}