下面是我的dologin.php的代码

header("content-type:text/html;charset=utf-8");

$mysqli = new mysqli('localhost','root','','test');

$mysqli->set_charset('utf8');

if ($mysqli->connect_errno)

{

die($mysqli->error);

}

$username = $_POST['username'];

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

$sql="SELECT * FROM test01 WHERE username=? and password=?" ;

$mysqli_stmt=$mysqli->prepare($sql);

$mysqli_stmt->bind_param('ss', $username, $password);

$con = $mysqli_stmt->execute();

     echo $mysqli_stmt->num_rows;

     print_r($mysqli_stmt);

sql和$con都没有错，数据库里面也是有数据的，从login页面传过来的数据也能对应到数据库里的数据，dologin执行的结果是0，$mysqli_stmt的内容是：

mysqli_stmt Object(    [affected_rows] => -1    [insert_id] => 0    [num_rows] => 0    [param_count] => 2    [field_count] => 4    [errno] => 0    [error] => 
   [sqlstate] => 00000    [id] => 1)