二级联动和三级联动的效果在web上很常见，在网上查了半天资料，写的都不是很清楚，无奈，自己写了个，使用PHP+ajax实现三级联动，以最常见的省市县三级联动为例！
CREATETABLEIFNOTEXISTS`province`(
`province_id`int(2)NOTNULLAUTO_INCREMENT,
`province_name`varchar(20)NOTNULL,255)">PRIMARYKEY(`province_id`)
)ENGINE=InnoDBDEFAULTCHARSET=utf8AUTO_INCREMENT=3;
INSERTINTO`province`(`province_id`,`province_name`)VALUES
(1,'安徽'),255)">(2,'浙江');
CREATETABLEIFNOTEXISTS`city`(
`city_id`int(4)NOTNULLAUTO_INCREMENT,255)">`city_name`varchar(20)NOTNULL,255)">`province_id`int(4)NOTNULL,255)">PRIMARYKEY(`city_id`)
)ENGINE=InnoDBDEFAULTCHARSET=utf8AUTO_INCREMENT=5;
INSERTINTO`city`(`city_id`,`city_name`,`province_id`)VALUES
(3,'南京',2),255)">(4,'徐州',2);
CREATETABLEIFNOTEXISTS`county`(
`county_id`int(4)NOTNULLAUTO_INCREMENT,255)">`county_name`varchar(20)NOTNULL,255)">`city_id`int(4)NOTNULL,255)">PRIMARYKEY(`county_id`)
INSERTINTO`county`(`county_id`,`county_name`,`city_id`)VALUES
对数据库说明：我创建了三张表，分别是省（province），市（city）,县（county）,插入了几条测试数据，当然你也可以设计一张表，效率当然没一张表好，所以不建议使用，看你个人习惯。
实现过程并不是很难，思路如下：
1)初始化所有的省份，这个可以直接从数据库中查询出来省份
2）当用户选择省份的时候触发事件，把当前的省份的id通过ajax发出请求传递到服务端的程序中3）服务端根据客户端的请求，查询数据库，并按照一定的格式返回给客户端4）客户端获取服务端的数据，进行必要的处理显示出来
创建select.PHP(代码简陋，只是实现功能而已，说明原理即可！)
1<!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML4.01Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
2<html>
3<head>
4<title>三级联动(作者：mckee-www.PHPddt.com)</title>
5<Metahttp-equiv="content-type"content"text/html;charset=UTF-8"/>
6<script>
7functioncreateAjax(){
8varxmlHttp=false;
9if(window.XMLHttpRequest){
10xmlHttp=newXMLHttpRequest();
11}elseifActiveXObject12try{
13xmlHttp=new("Msxml2.XMLHTTP");
14}catch(e){
15try{
16xmlHttp=newActiveXObject("Microsoft.XMLHTTP");
17catche18xmlHttp=false;
19}
20}
2122returnxmlHttp;
23}
24
25varajaxnull;
26functiongetCity(province_id){
27();
28ajax.onreadystatechange=function(){
29.readyState==430if(ajax.status==200){
31citiesresponseXMLgetElementsByTagName"city"32$('city').length=0;
33myoptiondocumentcreateElement"option"34myoption.value="";
35innerText"--请选择城市--"36$('city').appendChild(myoption);
37for(i=0;<length++){
38varcity_id=cities[i].childNodes[0].childNodes[0].nodeValue;
39city_name[].childNodes[1nodeValue40varmyoption=document.createElement("option");
41valuecity_id42myoption.innerText=city_name;
43$'city').appendChild44}
4546}
4748
49open"post","selectPro.PHP"true50ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
51send"province_id="+province_id52
5354
55getCounty56ajax=createAjax();
57onreadystatechange=function58if(ajax.readyState==4){
59status20060
61"county"62$('county').length=0;
6364myoption.value="";
65"--请选择县--"66$('county').appendChild(myoption);
6768varcity_id=cities[i].childNodes[0].childNodes[0].nodeValue;
6970varmyoption=document.createElement("option");
7172myoption.innerText=city_name;
73'county'74}
7576}
7778ajax.open("post","selectPro.PHP",true);
79setRequestHeader"Content-Type""application/x-www-form-urlencoded"80ajax.send("city_id="+city_id);
8182
83id84returndocument.getElementById(id);
8586
87</script>
88</head>
89<body>
90<formname="location">
91<selectname"province"onchange"getCitythis)">
92<optionvalue="">--请选择省份--</option>
93<?PHP
94$conn=MysqL_connect("localhost","root","");
95MysqL_select_db"test"96MysqL_query("setnamesutf8");
97$sql"select*fromprovince"
99while$resMysqL_fetch_assoc$result)){100?>
101<optionvalue="PHPecho$res['province_id'];?>">'province_name']?></option>102<?PHP
103}104?>
105</select>
106
107"city"onChange108<optionvalue="">--请选择城市--</option>
109110
111"county""county"112<optionvalue="">--请选择县--</option>
113114</form>
115</body>
116</html>
117118//禁止缓存(www.PHPddt.com原创)
119header"Content-type:text/xml;charset=utf-8"120header("Cache-Control:no-cache");
121//数据库连接
122$conn=MysqL_connect("localhost",255)">123124MysqL_query("setnamesutf8");
125
126if(!empty($_POST['province_id'])){
127
128$province_id=$_POST['province_id'];
129"select*fromcitywhereprovince_id={$province_id}"130$query=MysqL_query($sql);
131$info"<province>"132while($res=MysqL_fetch_assoc($query)){
133.="<city>"134$info.="<city_id>".$res['city_id']."</city_id>";
135"<city_name>"'city_name']."</city_name>"136$info.="</city>";
137138$info.="</province>";
139echo$info140}
141
142if(!empty($_POST['city_id'])){
143
144$city_id=$_POST['city_id'];
145"select*fromcountywherecity_id={$city_id}"146$query=MysqL_query($sql);
147148while($res=MysqL_fetch_assoc($query)){
149"<county>"150$info.="<county_id>".$res['county_id']."</county_id>";
151"<county_name>"'county_name'"</county_name>"152$info.="</county>";
153154$info.="</city>";
155156}
157?>
界面如下：
本代码在IE测试正常，欢迎大家提出建议和批评！
欢迎转载！原文地址:http://www.phpddt.com/php/769.html，转载请注明地址，谢谢！
