主题：不请教不行了

Dim pdr As DataRow = Nothing
Dim flag As Boolean = True
For Each dr As DataRow In DataTables("表A").Select("", "第一列")
    If pdr IsNot Nothing AndAlso pdr("第一列") <> dr("第一列") Then
        If flag = True Then
            msgbox(pdr("第一列"))
        End If
        flag = True
    End If
    If flag = True Then
        If dr("第二列") = "a" OrElse dr("第二列") = "b" Then
            flag = False
        End If
        If dr.IsNull("第三列") = False AndAlso dr("第三列") <> "a" AndAlso dr("第三列") <> "b" Then
            flag = False
        End If
        If dr.IsNull("第四列") AndAlso dr.IsNull("第五列") Then
            flag = False
        End If
    End If
    pdr = dr
Next