怎么先判断再修改或者增加记录

如何先判断再修改或者增加记录?
我想写一段代码,效果如下:   如果找到相同的出货单号码,则更新该出货单的内容,如果找不到该出货单,则增加一条出货单记录.
基本代码入下,具体要怎么修改?

<%

set   rs=server.CreateObject( "adodb.recordset ")
rs.Open   "select   *   from   huokuan   where   chuhuodan= "&request( "chudanhao "),conn,1,3
if   rs.eof   then
rs.AddNew
rs( "chuhuodan ")=request( "chudanhao ")
rs( "company ")=trim(request( "company "))
rs( "tel ")=trim(request( "tel "))


rs.Update
end   if
rs.Close
set   rs=nothing

%>

------解决方案--------------------
如果request( "chudanhao ")的值是数字的话
rs.Open "select * from huokuan where chuhuodan= "&request( "chudanhao "),conn,2,3

字符串的话

rs.Open "select * from huokuan where chuhuodan= ' "&request( "chudanhao ") & " ' ",conn,2,3