CREATE TRIGGER myTrigger ON myTable 
FOR UPDATE, INSERT
AS
UPDATE myTable SET t.E = t.A * t.B FROM test t, inserted i WHERE t.id=i.id

------解决方案--------------------
2L的方法不错：

DataTable _Table = new DataTable();  
           _Table.Columns.Add("A");  
           _Table.Columns.Add("B");  
           for (int i = 0; i != 100; i++)  
           {  
               _Table.Rows.Add(new object[] { i, i + 1 });  
           }  


添加计算列  
           _Table.Columns.Add("Sum(A*B)");  
           string _Expression = "convert(A,'System.Decimal')*convert(B,'System.Decimal')";  
           _Table.Columns["Sum(A*B)"].Expression = _Expression;  
           dataGridView1.DataSource=_Table;  


------解决方案--------------------
我写了一个例子：

//给dataGridView绑数据，我在这里动态的加了一些数据。
//A4输入公式，A3用公式计算。  
  private void button1_Click(object sender, EventArgs e)
       {
           DataSet t = new DataSet();
           System.Data.DataTable tab = new DataTable();
           DataColumn d = new DataColumn("A");
           DataColumn d1 = new DataColumn("A2");
           DataColumn d2 = new DataColumn("A3");
           DataColumn d3 = new DataColumn("A4");
          
          
           DataRow r = tab.NewRow();
           tab.Columns.Add(d);
           tab.Columns.Add(d1);
           tab.Columns.Add(d2);
           tab.Columns.Add(d3);
           r[0] = "100";
           r[1] = "33";

           tab.Rows.Add(r);
           DataRow r1 = tab.NewRow();

           r1[0] = "200";
           r1[1] = "333";
           DataRow r2 = tab.NewRow();

           r2[0] = "300";
           r2[1] = "3433";
           tab.Rows.Add(r2);
           t.Tables.Add(tab);
           this.dataGridView1.DataSource = t;
           this.dataGridView1.DataMember = t.Tables[0].TableName;