AJAX代表 A 同步 Ja vaScript和 X ML. AJAX是一种利用XML，HTML，CSS和Java Script创建更好，更快，更交互的Web应用程序的新技术.
传统的Web应用程序使用同步请求向服务器发送信息和从服务器发送信这意味着您填写一个表单，点击提交，然后从服务器获取新信息并进入新页面.
按下提交时使用AJAX， JavaScript将向服务器发出请求，解释结果并更新当前屏幕.从最纯粹的意义上讲，用户永远不会知道任何东西都被传送到服务器.
有关AJAX的完整学习，请参考 AJAX Tutorial.
为了清楚地说明使用Ajax和PHP从数据库访问信息是多么容易，我们将动态构建MySQL查询并在"ajax.html"上显示结果.但在我们继续之前，让我们做好基础工作.使用以下命令创建表.
注意 : 我们假设您有足够的权限执行以下MySQL操作.
CREATE TABLE `ajax_example` ( `name` varchar(50) NOT NULL, `age` int(11) NOT NULL, `sex` varchar(1) NOT NULL, `wpm` int(11) NOT NULL, PRIMARY KEY (`name`) )
现在使用以下SQL语句将以下数据转储到该表中.
INSERT INTO `ajax_example` VALUES ('Jerry', 120, 'm', 20);
INSERT INTO `ajax_example` VALUES ('Regis', 75, 'm', 44);
INSERT INTO `ajax_example` VALUES ('Frank', 45, 'm', 87);
INSERT INTO `ajax_example` VALUES ('Jill', 22, 'f', 72);
INSERT INTO `ajax_example` VALUES ('Tracy', 27, 'f', 0);
INSERT INTO `ajax_example` VALUES ('Julie', 35, 'f', 90);现在让我们的客户端HTML文件是ajax.html，它将具有以下代码
<html>
<body>
<script language = "javascript" type = "text/javascript">
<!--
//Browser Support Code
function ajaxFunction(){
var ajaxRequest; // The variable that makes Ajax possible!
try {
// Opera 8.0+, Firefox, Safari
ajaxRequest = new XMLHttpRequest();
}catch (e) {
// Internet Explorer Browsers
try {
ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
}catch (e) {
try{
ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
}catch (e){
// Something went wrong
alert("Your browser broke!");
return false;
}
}
}
// Create a function that will receive data
// sent from the server and will update
// div section in the same page.
ajaxRequest.onreadystatechange = function(){
if(ajaxRequest.readyState == 4){
var ajaxDisplay = document.getElementById('ajaxDiv');
ajaxDisplay.innerHTML = ajaxRequest.responseText;
}
}
// Now get the value from user and pass it to
// server script.
var age = document.getElementById('age').value;
var wpm = document.getElementById('wpm').value;
var sex = document.getElementById('sex').value;
var queryString = "?age=" + age ;
queryString += "&wpm=" + wpm + "&sex=" + sex;
ajaxRequest.open("GET", "ajax-example.php" + queryString, true);
ajaxRequest.send(null);
}
//-->
</script>
<form name = 'myForm'>
Max Age: <input type = 'text' id = 'age' /> <br />
Max WPM: <input type = 'text' id = 'wpm' />
<br />
Sex: <select id = 'sex'>
<option value = "m">m</option>
<option value = "f">f</option>
</select>
<input type = 'button' onclick = 'ajaxFunction()' value = 'Query MySQL'/>
</form>
<div id = 'ajaxDiv'>Your result will display here</div>
</body>
</html>注意 : 在Query中传递变量的方式是根据HTTP标准，并且具有formA.
URL?variable1=value1;&variable2=value2;
现在上面的代码会给你一个如下所示的屏幕
注意:这是虚拟屏幕，不起作用.
您的结果将显示在这里
现在您的客户端脚本已准备就绪.现在我们必须编写我们的服务器端脚本，它将从数据库中获取年龄，wpm和性别，并将其发送回客户端.将以下代码放入"ajax-example.php"文件中.
<?php
$dbhost = "localhost";
$dbuser = "dbusername";
$dbpass = "dbpassword";
$dbname = "dbname";
//Connect to MySQL Server
mysql_connect($dbhost, $dbuser, $dbpass);
//Select Database
mysql_select_db($dbname) or die(mysql_error());
// Retrieve data from Query String
$age = $_GET['age'];
$sex = $_GET['sex'];
$wpm = $_GET['wpm'];
// Escape User Input to help prevent SQL Injection
$age = mysql_real_escape_string($age);
$sex = mysql_real_escape_string($sex);
$wpm = mysql_real_escape_string($wpm);
//build query
$query = "SELECT * FROM ajax_example WHERE sex = '$sex'";
if(is_numeric($age))
$query .= " AND age <= $age";
if(is_numeric($wpm))
$query .= " AND wpm <= $wpm";
//Execute query
$qry_result = mysql_query($query) or die(mysql_error());
//Build Result String
$display_string = "<table>";
$display_string .= "<tr>";
$display_string .= "<th>Name</th>";
$display_string .= "<th>Age</th>";
$display_string .= "<th>Sex</th>";
$display_string .= "<th>WPM</th>";
$display_string .= "</tr>";
// Insert a new row in the table for each person returned
while($row = mysql_fetch_array($qry_result)) {
$display_string .= "<tr>";
$display_string .= "<td>$row[name]</td>";
$display_string .= "<td>$row[age]</td>";
$display_string .= "<td>$row[sex]</td>";
$display_string .= "<td>$row[wpm]</td>";
$display_string .= "</tr>";
}
echo "Query: " . $query . "<br />";
$display_string .= "</table>";
echo $display_string;
?>现在尝试在"Max Age"或任何其他框中输入有效值，然后单击Query MySQL按钮.
您的结果将显示在此处
如果您已成功完成本课程，那么您将了解如何串联使用MySQL，PHP，HTML和Javascript来编写Ajax应用程序.
