无刷新二级联动

我想做一个无刷新的二级联动,就是当选择一级的值时,不用刷新页面就可以出现第二级的相关内容,我做了个二级联动,可是他每选一次就会刷新一次页面,那样的话就会把前面表格中填的值清除掉
我的二级联动代码如下,哪位帮我改成无刷新的二级联动呀(要从数据库中搜索值)
<%
dim cid,coid
cid = request("cid") 'cid 大类id
coid = request("coid") 'coid 中类id
'set rs=server.createobject("adodb.recordset")
sql = "select * from FittingsType" '表一 大类表
rs.open sql,conn,1,1
strOption1 = "<option value='' selected >=请选择分类=</option>"
do while not rs.eof
if cstr(rs("id")) = cstr(cid) then
strOption1 = strOption1 & "<option value='" & rs("id") & "' selected>" & rs("typename") & "</option>"
else

strOption1 = strOption1 & "<option value='" & rs("id") & "'>" & rs("typename") & "</option>"

end if
rs.movenext <

<%
dim cid,coid
cid=Request("cid")
coid=Request("coid")
Set rs=CreateObject("adodb.recordset")
rs.open "Select * from FittingsType",conn,1,1 '获取大类数据
strOption1 = " <option value= ''>=请选择分类= </option >"
do while not rs.eof
if cstr(rs("id")) = cstr(cid) then
strOption1 = strOption1 & " <option value='" & rs("id") & "' selected >" & rs("typename") & "</option >"
else
strOption1 = strOption1 & " <option value= '" & rs("id") & "'>" & rs("typename") & "</option >"
end if
rs.movenext
loop
rs.close

rs.open "Select * from mode",conn,1,1 '获取小类数据
%>
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