参考 示例三

http://www.foxtable.com/help/topics/2403.htm

Select e.DataCol.Name
    Case "群组分类"
        If e.DataRow.IsNull("群组分类") Then
            e.DataRow("企业编号") = Nothing
        Else
            Dim lb As String = e.DataRow("群组分类")
            If e.DataRow("企业编号").StartsWith(lb) = False \'如果单据编号前缀不符
                Dim max As String
                Dim idx As Integer
                max = e.DataTable.Compute("Max(企业编号)","群组分类 = \'" & lb & "\' And [_Identify] <> " & e.DataRow("_Identify")) \'取得该类别的最大编号
                If max > "" Then \'如果存在最大编号
                    idx = CInt(max.Substring(2,3)) + 1 \'获得最大编号的顺序号,并加1
                Else
                    idx = 1 \'否则顺序号等于1
                End If
                e.DataRow("企业编号") = lb & Format(idx,"00")老师，0的前面我不需要字符。我刚开始学代码看不懂啊
            End If
        End If
End Select

 如下

Select e.DataCol.Name
    Case "群组分类"
        If e.DataRow.IsNull("群组分类") Then
            e.DataRow("企业编号") = Nothing
        Else
            Dim lb As String = e.DataRow("群组分类")
            Dim max As Integer
            Dim idx As Integer
            max = e.DataTable.Compute("Max(企业编号)","群组分类 = \'" & lb & "\' And [_Identify] <> " & e.DataRow("_Identify")) \'取得该类别的最大编号
            If max > "" Then \'如果存在最大编号
                idx = max + 1 \'获得最大编号的顺序号,并加1
            Else
                idx = 1 \'否则顺序号等于1
            End If
            e.DataRow("企业编号") = idx
        End If
End Select

NET Framework 版本：2.0.50727.3655
Foxtable 版本：2014.5.12.1
错误所在事件：表，通信，DataColChanged
详细错误信息：
Exception has been thrown by the target of an invocation.
Conversion from string "" to type \'Double\' is not valid.
Input string was not in a correct format.

老师，有错误提示

 呵呵，要这样改。

Select e.DataCol.Name
    Case "群组分类"
        If e.DataRow.IsNull("群组分类") Then
            e.DataRow("企业编号") = Nothing
        Else
            Dim lb As String = e.DataRow("群组分类")
            Dim idx As Integer
            idx = e.DataTable.Compute("Max(企业编号)","群组分类 = \'" & lb & "\' And [_Identify] <> " & e.DataRow("_Identify")) \'取得该类别的最大编号
            e.DataRow("企业编号") = idx + 1
        End If
End Select