Как выполнить внутреннее соединение после импорта excel в новый gridview без базы данных

---

у меня есть 3 gridview , 2 для импорта excel и 1 для внутреннего соединения
2 gridview для импорта сделан , но для внутреннего соединения еще нет , может мне помочь
спасибо

Что я уже пробовал:

public partial class Form1 : Form
    {
        public DataTable ReadExcel(string fileName, string fileExt)
        {
            string conn = string.Empty;
            DataTable dtexcel = new DataTable();
            if (fileExt.CompareTo(".xls") == 0)
                conn = @"provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + fileName + ";Extended Properties='Excel 8.0;HRD=NO;IMEX=1';"; //for below excel 2007  
            else
                conn = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + fileName + ";Extended Properties='Excel 12.0;HDR=NO';"; //for above excel 2007  
            using (OleDbConnection con = new OleDbConnection(conn))
            {
                try
                {
                    OleDbDataAdapter oleAdpt = new OleDbDataAdapter("select * from [Sheet1$]", con); //here we read data from sheet1  
                    oleAdpt.Fill(dtexcel); //fill excel data into dataTable  
                }
                catch { }
            }
            return dtexcel;
        }

        public Form1()
        {
            InitializeComponent();
           // BindGrid();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            string filePath = string.Empty;
            string fileExt = string.Empty;
            OpenFileDialog file = new OpenFileDialog(); //open dialog to choose file  
            if (file.ShowDialog() == System.Windows.Forms.DialogResult.OK) //if there is a file choosen by the user  
            {
                this.richTextBox1.Text = file.FileName;
                filePath = file.FileName; //get the path of the file  
                fileExt = Path.GetExtension(filePath); //get the file extension  
                if (fileExt.CompareTo(".xls") == 0 || fileExt.CompareTo(".xlsx") == 0)
                {
                    try
                    {
                        DataTable dtExcel = new DataTable();
                        dtExcel = ReadExcel(filePath, fileExt); //read excel file  
                        dataGridView1.Visible = true;
                        dataGridView1.DataSource = dtExcel;
                    }
                    catch (Exception ex)
                    {
                        MessageBox.Show(ex.Message.ToString());
                    }
                }
                else
                {
                    MessageBox.Show("format file harus .xls atau .xlsx .", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Error); //custom messageBox to show error  
                }
            }

        }
                                    
        private void button3_Click(object sender, EventArgs e)
        {
            string filePath = string.Empty;
            string fileExt = string.Empty;
            OpenFileDialog file = new OpenFileDialog(); //open dialog to choose file  
            if (file.ShowDialog() == System.Windows.Forms.DialogResult.OK) //if there is a file choosen by the user  
            {
                this.richTextBox2.Text = file.FileName;
                filePath = file.FileName; //get the path of the file  
                fileExt = Path.GetExtension(filePath); //get the file extension  
                if (fileExt.CompareTo(".xls") == 0 || fileExt.CompareTo(".xlsx") == 0)
                {
                    try
                    {
                        DataTable dtExcel = new DataTable();
                        dtExcel = ReadExcel(filePath, fileExt); //read excel file  
                        dataGridView2.Visible = true;
                        dataGridView2.DataSource = dtExcel;
                    }
                    catch (Exception ex)
                    {
                        MessageBox.Show(ex.Message.ToString());
                    }
                }
                else
                {
                    MessageBox.Show("format file harus .xls atau .xlsx .", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Error); //custom messageBox to show error  
                }
            }
        }

---