主题：[求助]网络编程的自动编号问题

Dim bh As String
Dim dr As DataRow = e.DataRow
Dim pf As String
Dim max As String
Dim cmd As New SQLCommand
Dim dt As DataTable

pf = Format(dr("Riqi"),"yyMMdd") '获得编号的前缀

cmd.C
cmd.commandText = "Select top 1 Danhao,* From Bill_Shou Where Danhao Like  '" & pf & "*'"
dt = cmd.ExecuteReader
dr = dt.DataRows(0)
If dr("Danhao") Is Nothing Then
    bh = Format(dr("Danhao"),"yyMMdd001")
Else
    max = dr("Danhao")
    max = cint(max.Substring(7,3)) + 1
    bh = pf & format(max,"000")
End If

e.DataRow("Danhao") = bh

以上代码目的是如果是今天的第一单，单号就是121019001，第二单是121019002，依次类推。

运行报错，错误代码为

Exception has been thrown by the target of an invocation.

狐爸来帮下忙吧，这个在系统里面，无法传附件的

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点击浏览该文件:网络变成自动编号问题.rar

目的就是按照日期，自动获取一个单号

比如今天是2012-10-19

获取的第一个是121019001

第二个是121019002

依次类推

ACCESS测试正常，在SQL SERVER2000下，在这句出错

max = max.Substring(6,3)

错误提示是
Exception has been thrown by the target of an invocation.