数据库三级联动怎么做

   这么做到选择国家的时候省市和市区显示  选择市区的时候出现省市和国家的选择  。   

<form action="city.php?module=add" method="Post" name='frmdirection' id='frmdirection'>	<input type="hidden" name="id" value="{$data.id}" id="uid"/>    <table  width="100%" border="0" cellpadding="0" cellspacing="0" class="ttbb2">		<tr>        <td width="40%" align="right" bgcolor="#e9f4ff"><strong>地区/行政区域</strong></td>        <td>		<input type="radio" name="pos_occu" value="2" {if $data.parentid eq "" or $data.parentid neq "99999"}checked="checked"{/if}  onclick="clickRadio()"/>地区        <input type="radio" name="pos_occu" value="0" {if $data.parentid eq "" or $data.parentid neq '99999'}checked="checked"{/if}  onclick="clickRadio()"/>省份        <input type="radio" name="pos_occu" value="1" {if $data.parentid eq '99999'}checked="checked"{/if} onclick="clickRadio()"/>国家                 </td>        </tr>        <tr>        <td width="40%" align="right" bgcolor="#e9f4ff"><strong>名称</strong></td>        <td><input type ="text"  class="txt150"   name = "data[name]" value="{$data.name}"  id="name">          </td>        </tr>        <tr  >        <td width="40%" align="right" bgcolor="#e9f4ff"><strong>所属国家</strong></td>        <td>        <select name = "data[parentid]"   id="parentid"  {if $data.parentid neq '99999'}style="display:block"{else}style="display:none"{/if}>          	{foreach from=$parent item=item key=index}            <option value="{$item.id}"            {if $item.id eq $data.parentid && $data.parentid neq ""}            selected="selected"            {/if}            >{$item.name} </option>            {/foreach}          </select>          </td>        </tr>  		<tr >        <td width="40%" align="right" bgcolor="#e9f4ff"><strong>所属省份</strong></td>        <td>        <select name = "data[parentid]"   id="parentid"  {if $data.parentid neq "99999"}style="display:block"{else}style="display:none"{/if}>          	{foreach from=$parent item=item key=index}            <option value="{$item.id}"            {if $item.id eq $data.parentid && $data.parentid neq ""}            selected="selected"            {/if}            >{$item.name} </option>            {/foreach}          </select>          </td>        </tr>  </table></form>

回复讨论(解决方案)

没明白 你想干什么 
是数据库设计不好 
还是代码不会写