主题：为何这两组代码同时放在一起不执行

楼主传错附件了：

推测了你的逻辑可能是这样的：

Dim dr As DataRow =e.DataRow
Select e.DataCol.Name
    Case "日期","序号"
        If dr.IsNull("日期") OrElse dr.isnull("序号") Then
            dr("编号") = Nothing
        Else
            Dim drs As List(of DataRow) =e.DataTable.Select("日期 =#" & dr("日期") & "# and 序号 ='" & dr("序号") & "'" ,"_Identify")
            Dim i As Integer
            For Each tr As DataRow In drs
                Dim d As Date = tr("日期")
                Dim xh As Integer =tr("序号")
                Dim bh As String =  Format(d,"yyyyMMdd")  & format(xh,"000") '生成编号的前缀
                i =i+1
                tr("编号") = bh & format(i,"000")
            Next
        End If
    Case "机号"
        If dr.IsNull("机号") = False Then
            Dim drs As List (of DataRow) = e.DataTable.Select("[机号] Is null And [ID] < " & e.DataRow("ID") & "")
            For Each dr1 As DataRow In drs
                dr1("机号") = e.NewValue
            Next
        End If
End Select