登录页面：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script src="../../jquery-1.11.2.min.js"></script>
</head>
<body>
<div>用户名：<input type="text" id="uid" /></div>
<div>密码：<input type="text" id="pwd" /></div>
<input type="button" value="登录" id="btn" />
</body>
<script type="text/javascript">
$("#btn").click(function(){
var uid = $("#uid").val();
var pwd = $("#pwd").val();
$.ajax({
url:"loginchuli.php",
data:{u:uid,p:pwd},
type:"POST",
dataType:"TEXT",
success: function(data){
if(data.trim()=="OK")//trim的目的：去处理页面的空格
{
window.location.href="main.php";
}
else
{
alert("用户名或密码错误");
}
}
});
})
</script>
</html>
处理页面：
<?php
session_start();
include("../DBDA.class.php");
$db = new DBDA();
$uid = $_POST["u"];
$pwd = $_POST["p"];
$sql = "select password from login where username='{$uid}'";
$mm = $db->StrQuery($sql);
if($mm==$pwd && $pwd!="")
{
$_SESSION["uid"]=$uid;
echo "OK";
}
else
{
echo "NO";
}