如何将excel导入datagrid然后将特定列保存到mysql数据库

Question

我想将我导入的excel文件的特定列添加到数据网格视图中。但问题是，当我点击保存时，我收到以下错误：

  

＆＃34;无法转换类型为＃System ;DBNull＆＃39;的对象输入   ＆＃39; System.String＆＃39;＆＃34;

我总共有9列，我只想添加3列。这是我的代码：

 private void button1_Click(object sender, EventArgs e)
    {
        OpenFileDialog dlg = new OpenFileDialog();
        dlg.Filter = "Excel Files|*.xls;*.xlsx;*.xlsm";
        if (dlg.ShowDialog() == DialogResult.OK)
        {
            label1.Text = dlg.FileName.ToString();
            string path = label1.Text;

            string conn = @"Provider=Microsoft.ACE.OLEDB.12.0;" + "Data Source=" + path + ";" + "Extended Properties=" + "\"" + "Excel 12.0;HDR=YES;" + "\"";
            OleDbConnection conn1 = new OleDbConnection(conn);

            OleDbDataAdapter dataAdapter = new OleDbDataAdapter("select * from [Sheet1$]", conn1);


            DataTable dataSet = new DataTable();
            dataAdapter.Fill(dataSet);
            dataGridView1.DataSource = dataSet;
        }

    }

    private void button2_Click(object sender, EventArgs e)
    {
        using (MySqlConnection conn = new MySqlConnection(cs))
        {
            MySqlCommand command = new MySqlCommand();
            MySqlDataReader reader;

            MySqlCommand command2 = new MySqlCommand();
            //MySqlDataReader reader1;
            using (MySqlCommand cmd = new MySqlCommand())
            {
                cmd.Connection = conn;
                conn.Open();
                for (int i = 0; i < dataGridView1.Rows.Count; i++)
                {
                    Boolean Empty = true;
                    for (int j = 0; j < dataGridView1.Columns.Count; j++)
                    {
                        if ((string)dataGridView1.Rows[i].Cells[j].Value != "")
                        {
                            Empty = false;
                            StrQuery = @"INSERT Ignore INTO course(Code,Course,Major) VALUES ('"
                                   + dataGridView1.Rows[i].Cells["Course Code"].Value + "','"
                                   + dataGridView1.Rows[i].Cells["Course"].Value + "','"
                                   + dataGridView1.Rows[i].Cells["Major"].Value + "')";
                            cmd.CommandText = StrQuery;
                            cmd.ExecuteNonQuery();
                        }
                    }
                    if (Empty)
                    {
                        dataGridView1.Rows.RemoveAt(i);
                        i--;
                    }
                }
            }
            MessageBox.Show("Successfully Added!");
        }

    }