如何判断ASP数据库里面内容是否存在

<%

if request.querystring("action")="dh" then

    set rs=server.createobject("adodb.recordset")

    sql="select * from mc_paidui where uid="&server.HTMLEncode(trim(request.form("uid")))&" and datetime='"&request.form("datetime")&"'"

    rs.open sql,conn,1,3

    if rs.eof then

        rs.addnew

        rs("cart")=trim(request.form("cart"))

        rs("uid")=server.HTMLEncode(trim(request.form("uid")))

        rs("uniacid")=server.HTMLEncode(trim(request.form("uniacid")))

        rs("sh")=server.HTMLEncode(trim(request.form("sh")))

        rs("datetime")=trim(request.form("datetime"))

        rs.update

        rs.close

        sql="select * from ims_mc_members where uid="&request.form("uid")

        rs.open sql,conn,1,3

        rs("credit1")=trim(request.form("credit1"))

        rs.update

        response.Write "<script language=javascript>alert('兑换成功！')window.location.href='"&request.serverVariables("HTTP_REFERER")&"'</script>"

    end if

    rs.close

    set rs=nothing

    conn.close

    set conn=nothing

end if

%>

<p><%set rs=server.createobject("adodb.recordset")<br>sql="select * from wzadd where title="&request("title")<br>rs.open sql,conn,1,1</p> <p>if rs.eof then%></p> <p><script language="javascript"><br>alert(" 不存在")<br></script></p> <p><%else%></p> <p><script language="javascript"><br>alert(" 存在")<br></script></p> <p><%end if%></p>

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