解决检验手机号码已存在的问题！有源码

<%
dim rs,sql
set rs=server.createobject("adodb.recordset")
rs.open "select * from cdb where tel='"&request.form("tel")&"'",conn,1,3
if rs.bof and rs.eof then
response.write "<script>alert('该电话号码已存在！');history.go(-1);</script>"
response.end
end if
rs.addnew
rs("user")=request.form("user")
rs("tel")=request.form("tel")
rs("dt")=now()
rs("productID")=request.form("productID")
rs("ip")=request.ServerVariables("remote_addr")
rs("url")=Request.ServerVariables("HTTP_REFERER")
rs.update
rs.close
set rs=nothing
conn.close
set conn=nothing
%>
检查手机号是否重复哪位朋友能解答一下问题在哪？
是不是这段有问题rs.open "select * from cdb where tel='"&request.form("tel")&"'",conn,1,3