主题：帮忙注释下每行代码

 看懂这部分即可，下面的不用看

 找到当前行的上一行

        dr = e.DataTable.Find("[_SortKey] < " & mr("_SortKey") & " And [产品] = '" & mr("产品") & "'", "[_SortKey] Desc")
        If dr Is Nothing Then '如果没找到，直接计算
            jk =  DataTables("例子二").SQLCompute("Sum(入库)","[_SortKey] < " & mr("_SortKey") & " And 产品 = '" & mr("产品") & "'")
            ck =  DataTables("例子二").SQLCompute("Sum(出库)","[_SortKey] < " & mr("_SortKey") & " And 产品 = '" & mr("产品") & "'")
            mr("库存") = e.DataRow("入库") - e.DataRow("出库") + jk - ck
            dr = mr
        End If

 计算当前行一下的所有行，等于上一行的库存+本行入库-本行出库
        drs = e.DataTable.Select("[_SortKey] >= " & dr("_SortKey") & " And [产品] = '" & dr("产品") & "'", "[_SortKey]")
        For i As Integer = 1 To drs.Count - 1
            drs(i)("库存") = drs(i-1)("库存") + drs(i)("入库") - drs(i)("出库")
        Next