PHP-1.数据库连接与登陆

 <?php
 //数据库信息
 $servername = "localhost";
 $username = "root";
 $password = "****";
 $dbname="login";
 /*
  *  mysql_select_db('l');
  *  mysql_query('set names utf8');
  */
 //打开session
 session_start();
 //判断账号密码是否被赋值
 if (isset($_POST['user']) && isset($_POST['pass'])) {
     $user = $_POST['user'];
     $pass = $_POST['pass'];
     //建立一个数据库连接
     $conn = mysql_connect($servername,$username,$password);
     /* 测试
      * if($conn)
      *  echo "连接成功";
      *  else die("连接失败".mysql_error());
      */ }
     //检查是否启动并给出提示
     if (!$conn) {
         die("connection failed:" . $conn->connect_error);
     }
     //指定一个数据库
     $db_select=mysql_select_db($dbname,$conn);
     //验证内容是否与数据库记录吻合
     $sql_L = "SELECT * FROM l WHERE (username='$user') AND (password='$pass')";
     //执行上面的sql语句并赋值给$r
     $r = mysql_query($sql_L,$conn);
     //将查到的结果数赋值$result
     $result = mysql_num_rows($r);
     //判断是否有对应记录
     if ($result>0) {
         echo "<script type='text/javascript'>alert('欢迎')</script>";
     } else
         echo "<script type='text/javascript'>alert('密码错误')</script>";
     //关闭数据库连接
     mysql_close($conn);

 ?>