我不能解决这个错误：mysqli_num_rows（）期望参数1是mysqli_result，布尔在

Question

给出我只是不能解决问题。我是编程初学者，所以我希望能够得到帮助。

if (count($errors) == 0) { 
     $password = md5($password); 
     $query = "SELECT * FROM users WHERE username='$username' AND password='$password'"; 
     $result = mysqli_query($db, $query); 

     if (mysqli_num_rows($result) == 1) { 
      $_SESSION['username'] = $username; 
      $_SESSION['success'] = "You are now logged in"; 
      header('location: index.php'); 
     }else { 
      array_push($errors, "Wrong username or password."); 
     } 
    } 
} 

Answer 1

问题是，如果没有返回任何内容，“SELECT”查询返回false。如果用户名和密码不正确，请拨打$result=false。 mysqli_num_rows只接受mysqli_result对象作为参数。

你可以改变你的if语句是：

if ($result){ 
    if (mysqli_num_rows($result) == 1) { 
     $_SESSION['username'] = $username; 
     $_SESSION['success'] = "You are now logged in"; 
     header('location: index.php'); 
    } 
}else { 
    array_push($errors, "Wrong username or password."); 
}