private void addtotal()
        {
            this.dataGridView1.Columns.Add("total", "总和");
            Dictionary<string, int> total = new Dictionary<string, int>();
            foreach (DataGridViewRow dr in this.dataGridView1.Rows)
            {
                if (dr.Cells[0].Value != null)
                {
                    string name = dr.Cells[0].Value.ToString();

                    int t = Convert.ToInt32(dr.Cells[2].Value.ToString());
                    if (total.ContainsKey(name))
                        total[name] += t;
                    else
                        total.Add(name, t);
                }

            }
            foreach (DataGridViewRow dr in this.dataGridView1.Rows)
            {
                if (dr.Cells[0].Value != null)
                {
                    string name = dr.Cells[0].Value.ToString();
                    if (total.ContainsKey(name))
                        dr.Cells[3].Value = total[name];
                    else
                        dr.Cells[3].Value = 0;
                }
            }

        }

Dim sumObject As Object
    sumObject = table.Compute("Sum(Total)", "EmpID = 5")