php接收post数据并写入mysql有关问题

CREATE TABLE `student` (
  `id` int(10) unsigned NOT NULL auto_increment,
  `xid` varchar(20) NOT NULL,
  `name` varchar(20) NOT NULL,
  `email` varchar(100) NOT NULL,
  `address` varchar(100) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

// 连接数据库  
[email protected]_connect("数据库ip","帐号","密码")  or die(mysql_error());  
@mysql_select_db('数据库名',$conn) or die(mysql_error());  

$action = isset($_REQUEST['action'])? $_REQUEST['action'] : '';

if($action=='add'){
    $xid = isset($_POST['xid'])? mysql_escape_string($_POST['xid']) : '';
    $name = isset($_POST['name'])? mysql_escape_string($_POST['name']) : '';
    $email = isset($_POST['email'])? mysql_escape_string($_POST['email']) : '';
    $address = isset($_POST['address'])? mysql_escape_string($_POST['address']) : '';

    if($xid=='' 
------解决思路----------------------
 $name=='' 
------解决思路----------------------
 $email=='' 
------解决思路----------------------
 $address==''){
        echo 'please input data';
        exit();
    }

    $sqlstr = "insert into student(xid,name,email,address) values('".$xid."','".$name."','".$email."','".$address."')";
    mysql_query($sqlstr) or die(mysql_error());

    header('location:postdemo.php');

}else{
?>


 
  
  
 

 
  

     $sqlstr = "select * from student order by id";
    $query = mysql_query($sqlstr) or die(mysql_error());
    $result = array();
    while($thread=mysql_fetch_assoc($query)){
        $result[] = $thread;
    }

    if($result){
        echo '';
        echo '';
        foreach($result as $row){
            echo '';
            echo '';
            echo '';
            echo '';
            echo '';
            echo '';
            echo '';
        }
        echo '
NO
学生id
学生名字
学生邮箱
学生地址
'.$row['id'].'
'.$row['xid'].'
'.$row['name'].'
'.$row['email'].'
'.$row['address'].'
';
    }

 ?>
  
 

}
?>