=====前台ajax
<!DOCTYPE html>
<html lang="en">
<head>
???<meta charset="UTF-8">
???<title>Title</title>
???<script src="../wenjian/jquery-2.2.3.min.js"></script>
</head>
<body>
<select id="sheng">
???<option>请选择</option>
</select>
<select id="shi">
???<option >请选择</option>
</select>
<select id="qu">
???<option >请选择</option>
</select>
</body>
</html>
<script>
???$.ajax({
???????data: {parent_id: 0}, //发送的数据
???????dataType: "json", //返回值的类型 text为string型
???????type: ‘post‘, ??//发送请求的方法(get)
???????url: ‘sheng_l.php‘,//发送请求的地址
???????success: function (data) {//发送成功时的回调函数
???// ???????????console.log(data);
???????????for (var i in data) {
???????????????$("#sheng").append("<option value=‘"+ data[i][2] +"‘>" + data[i][1] ?+"</option>")
???????????}
???????}
???})
???$(document).ready(function () {
???????$("#sheng").change(function () {
???????????$("#shi").get(0).options.length= 1;
// ???????????$("#qu").get(0).options.length= 1;
???????????var data = $("#sheng").find("option:selected").val();
???????????$.ajax({
???????????????data:{parent_id:data},
???????????????type:"post",
???????????????dataType:"json",
???????????????url:"sheng_l.php",
???????????????success:function (data) {
???????????????????for(var i in data){
???????????????????????$("#shi").append("<option value=‘" + data[i][2] +"‘>" + data[i][1] +"</option>")
???????????????????}
???????????????}
???????????})
???????})
???})
???$(document).ready(function () {
???????$("#shi").change(function () {
???????????$("#qu").get(0).options.length= 1;
???????????var data = $("#shi").find("option:selected").val();
???????????$.ajax({
???????????????data:{parent_id:data},
???????????????type:"post",
???????????????dataType:"json",
???????????????url:"sheng_l.php",
???????????????success:function (data) {
???????????????????for (var i in data){
???????????????????????$("#qu").append("<option value=‘" +data[i][2] +"‘>" +data[i][1] +"</option>")
???????????????????}
???????????????}
???????????})
???????})
???})
==============后台处理页面代码
<?php
/**
* Created by fcc
* User: Administrator
* Date: 2017/10/29
* Time: 20:56
*/
require_once "../wenjian/DBDA.class.php";
$db = new DBDA();
$sql = "select * from region WHERE father_id = {$_POST[‘parent_id‘]}";
$result = $db->Query($sql);
echo json_encode($result);
转自：迪恩杰
http://www.cnblogs.com/dej-11/p/7753176.html
ajax 三级联动写法
原文地址：http://www.cnblogs.com/leader007/p/7753591.html