主题：求教一个比较复杂的录入计算问题

Dim dta As DataTable = DataTables("表A")
Dim dtb As DataTable = DataTables("表B")
Dim dr As DataRow = dta.DataRows(1)
msgbox(dr("产品编号"))
Dim sum As Double = 0
Dim bdrs = dtb.Select("产品编号 = '" & dr("产品编号") & "'")
For Each bdr As DataRow In bdrs
    dr(bdr("使用项目")) = bdr("数量")
    sum += bdr("数量")
Next
If sum > dr("数量") Then
    bdrs(bdrs.count-1)("使用库存量") = sum - dr("数量")
End If