参考帮助中的下列代码，没成功

If e.DataCol.Name = "型号" Then \'如果内容发生变动的是品名列

    If e.NewValue Is Nothing Then \'如果新值是空白,也就是品名列的内容为空

        e.DataRow("成本") = Nothing \'那么清空此行单价列的内容

    Else

        Dim dr As DataRow

        \'否则在产品表查找同名的产品行,将找到的行赋值给变量dr

        dr = DataTables("采购明细").SQLFind("[型号] = \'" & e.NewValue & "\'")

        If dr IsNot Nothing Then \'如果找到了同名的产品行,也就是dr不是Nothing

            e.DataRow("成本") = dr("单价")

        End If

    End If

End If

. 如果列名不同，或者只需复制部分列，可以参考下面的代码：

If e.DataCol.Name = "逻辑列名" AndAlso e.DataRow("逻辑列名") = True Then
    Dim nma() As String = {"A1","A2","A3","A4"} \'A表数据来源列
    Dim nmb() As String = {"B1","B2","B3","B4"} \'B表数据接收列
    Dim dr As DataRow = DataTables("表B").AddNew
    For i As Integer = 0 To nma.Length - 1
        dr(nmb(i)) = e.DataRow(nma(i))
    Next
End If

Dim Sum2 As Double = DataTables("订单").Compute("Sum(数量)", "产品 = \'PD01\'")这样的计算。

If e.DataCol.Name = "合同号"   Then
    Dim nma() As String = {"合同号","客户","金额"} \'A表数据来源列
    Dim nmb() As String = {"单据号","客户","借方"} \'B表数据接收列
    Dim dr As DataRow = DataTables("应收账款").AddNew
    For i As Integer = 0 To nma.Length - 1
        dr(nmb(i)) = e.DataRow(nma(i))
    Next
End If

上述代码中第二行的“金额”应该是统计每个合同号的金额，就是这个“金额”应如何写代码不知道