求救:怎么才能把做的二级联动菜单跟数据库相关联

我数据库中有两个表表A(m_id int not null primary key auto_increment,
                       m_name varchar(255) not null)
                   表B(n_id  int not null primary key auto_increment,
                       m_id int not null,
                       n_name varchar(255) not null)
第一个下拉列表全是表A的m_name,第二个下拉列表全是表B的n_name,
但是当我点击第一个下拉列表的m_name时,在第二个下拉列表的n_name也会随着变化
??

解决方案 »

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Ajax 的干活，去 Ajax 区一搜一大把！
第一个产生个事件,用被选的ID查第二张表,
很多方法,不过还是AJAX好
不用刷新
那位高手可以帮我看下,那出错了
<%@page pageEncoding="GB2312"%>
<%@page contentType="text/html; charset=gb2312"%>
<%request.setCharacterEncoding("gb2312");%>
<%@ page language="java" import="java.util.*,javax.sql.DataSource,java.sql.*"%>
<jsp:useBean id="cartype" class="beans.connBean" scope="session"/>
<%
if((request.getParameter("submit")!="")&&(request.getParameter("submit")!=null)){
  int rs;
  String cars_id=request.getParameter("cars_id");
   String cartype_name=request.getParameter("cars_type_name");
  String cars_comp=request.getParameter("cars_comp");
  String service_price=request.getParameter("service_price");
  String et_price=request.getParameter("et_price");
  out.println("输入数据库的车id :"+cars_id);
  out.println("输入数据库的车类型名 :"+cartype_name);
  String sql="insert into cars_type(cars_id,cars_type_name)values('"+cars_id+"','"+cartype_name+"')";
  rs=cartype.executeUpdate(sql);
  if(rs>0){
%>
  <p>添加成功!</p>
<%  }else{  %>
  <p>添加失败 !</P><% }
   }
%><script language="javascript">
function onselect(formname,value) {
//alert("adfasd");
write(value);
formname.action ="addcomp.jsp?cars_id="+value;
//document.write(formname.action);
//alert(document.formname.action);
alert(formname.action);
//formname.submit(); }
</script><html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
<title>添加配件信息</title>
</head>
<body topmargin="0" leftmargin="0" bottommargin="0" rightmargin="0">
<table width="100%" border="0" cellpadding="0" cellspacing="0">
<form action="addcomp.jsp" name="addcomp" style="margin=0px;" target="_self" method="post">
  <tr> <td height="35" align="center">车名</td>
      <td height="35" align="center">
<%
       String sq="select cars_id,cars_name from cars_name";
       ResultSet rr=cartype.executeQuery(sq);
%>
      <select name="cars_id" onchange="javascript:onselect(addcomp,this.value);">
      <option>请选择</option>
<%
       while(rr.next()){
%>
      <option value=<%=rr.getString("cars_id")%> ><%=rr.getString("cars_name")%></option>
<%   }   %>
      </select>
     </td>
     <td height="35" align="center">车类型名:<select name="carstype_id">
     <option>请选择</option>
<%   String carid=request.getParameter("cars_id");
     out.println("adfasffasdf");
     out.println(carid);
     if(carid!=null || carid!="")
        {
           String carsql="select * from cars_type where cars_id'"+carid+"'";
           ResultSet carrs=cartype.executeQuery(carsql);
           while(carrs.next())
              {
%>
           <option value="<%=carrs.getString("cars_type_id") %> > <%=carrs.getString("cars_type_name") %> </option>
<%               }
       }           %>     </td>
<td height="35" align="center">配件名称：<input type="text" name="carscomp_name"></td>
<td height="35" align="center">维修价:<input type="text" name="service_price"></td>
<td height="35" align="center">市场价:<input type="text" name="et_price"></td>
  </tr>
  <tr>
     <td height="35" colspan="3" align="center"><input type="submit" value="添加" name="submit">
     </td>
  </tr>
</form>
</table>
</body>
</html>
<%@page pageEncoding="GB2312"%>
<%@page contentType="text/html; charset=gb2312"%>
<%request.setCharacterEncoding("gb2312");%>
<%@ page language="java" import="java.util.*,javax.sql.DataSource,java.sql.*"%>
<jsp:useBean id="cartype" class="beans.connBean" scope="session"/>
<%
if((request.getParameter("submit")!="")&&(request.getParameter("submit")!=null)){
  int rs;
  String cars_id=request.getParameter("cars_id");
  String carstype_id=request.getParameter("carstype_id");
   String carcomp_name=request.getParameter("carscomp_name");

  String service_price=request.getParameter("service_price");
  String et_price=request.getParameter("et_price");
  out.println("输入数据库的车id :"+cars_id);
  out.println("输入数据库的车类型名 :"+cartype_name);
  String sql="insert into cars_component(cars_id,cars_type_id,cars_comp_name,service_price,et_price)values('"+cars_id+"','"+carstype_id+"','"+carcomp_name+"','"+service_price+"','"+et_price+"'";
  rs=cartype.executeUpdate(sql);
  if(rs>0){
%>
  <p>添加成功!</p>
<%  }else{  %>
  <p>添加失败 !</P><% }
   }
%><script language="javascript">
function onselect(formname,value) {
//alert("adfasd");
alert(value);
formname.action ="addcomp.jsp?cars_id="+value;
//document.write(formname.action);
//alert(document.formname.action);
alert(formname.action);
//formname.submit(); }
</script><html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
<title>添加配件信息</title>
</head>
<body topmargin="0" leftmargin="0" bottommargin="0" rightmargin="0">
<table width="100%" border="0" cellpadding="0" cellspacing="0">
<form action="addcomp.jsp" name="addcomp" style="margin=0px;" target="_self" method="post">
  <tr> <td height="35" align="center">车名</td>
      <td height="35" align="center">
<%
       String sq="select cars_id,cars_name from cars_name";
       ResultSet rr=cartype.executeQuery(sq);
%>
      <select name="cars_id" onchange="javascript:onselect(addcomp,this.value);">
      <option>请选择</option>
<%
       while(rr.next()){
%>
      <option value=<%=rr.getString("cars_id")%> ><%=rr.getString("cars_name")%></option>
<%   }   %>
      </select>
     </td>
     <td height="35" align="center">车类型名:<select name="carstype_id">
     <option>请选择</option>
<%   String carid=request.getParameter("cars_id");
     out.println("adfasffasdf");
     out.println(carid);
     if(carid!=null || carid!="")
        {
           String carsql="select * from cars_type where cars_id'"+carid+"'";
           ResultSet carrs=cartype.executeQuery(carsql);
           while(carrs.next())
              {
%>
           <option value="<%=carrs.getString("cars_type_id") %> > <%=carrs.getString("cars_type_name") %> </option>
<%               }
       }           %>
    </select>
     </td>
<td height="35" align="center">配件名称：<input type="text" name="carscomp_name"></td>
<td height="35" align="center">维修价:<input type="text" name="service_price"></td>
<td height="35" align="center">市场价:<input type="text" name="et_price"></td>
  </tr>
  <tr>
     <td height="35" colspan="3" align="center"><input type="submit" value="添加" name="submit">
     </td>
  </tr>
</form>
</table>
</body>
</html>