PHP登陆问题

我的问题是才开始不管输入什么都正确 现在该后 是输入什么都不正确 我建2数据库 才第一个网站登陆管用 在第2网站登陆就会出现问题 代码如下
<?php

include "lianjie_jb.php";

session_start();

if($tijiao == "提交"){

$user_name = $_POST['user_name'];

$pass_word = md5($_POST['pass_word']);

$sql = "select count(*) as total from user_info where user_name = '$user_name'and pass_word =

'$pass_word'";

$r = mysql_query($sql);

$b = mysql_fetch_array($r);

$c = $r['total'];

if($c>=1){

$_SESSION['user_name'] = $b[user_name];

$_SESSION['id'] = $b[id];

$_SESSION['user_bb'] = $b[user_bb];

$_SESSION['user_qq'] = $b[user_qq];

$_SESSION['user_dj'] = $b[user_dj];

$_SESSION['nickname'] = $b[nickname];

$_SESSION['man'] = $b[man];