Question

i have already searched everywhere but could not find a solution for the problem.
i have a login script in php.When there are no matches in the database for user entered values, an error message is displayed.But also another warning is being thrown.

Warning: mysqli_num_rows() expects parameter 1 to be mysqli, 
boolean given in C:\xampp\htdocs\index.php on line 26

Here’s the code. i know that a similar question has been asked many times,but none of them could provide me the solution.Here’s the entire code.

    <?php

    session_start();
    require_once('connectionvariables.php');
    $error_msg = "";

    if(!isset($_SESSION['user_id']))
     {
      if(!empty($_COOKIE['user_id']) && !empty($_COOKIE['username']))
        {
          $_SESSION['user_id'] = $_COOKIE['user_id'];
          $_SESSION['username'] = $_COOKIE['username'];
     }
     else
      {
        if(isset($_POST['submit']))
         {
          $dbc = mysqli_connect(DB_HOST,DB_USER,DB_PASSWORD,DB_NAME);
        $user_username = mysqli_real_escape_string($dbc,trim($_POST['username']));
        $user_password = mysqli_real_escape_string($dbc,trim($_POST['password']));

        if(!empty($user_username) && !empty($user_password))
        {
            $query = "SELECT user_id,username FROM mismatch_user WHERE username =       '$user_username' AND password = SHA('$user_password')";
            $data = mysqli_query($dbc,$query); 
            if(mysqli_num_rows($data) == 1)
            {
                $row = mysqli_fetch_array($data);
                $_SESSION['user_id'] = $row['user_id'];
                $_SESSION['username'] = $row['username'];
                setcookie('user_id',$row['user_id'],time() + ( 60 * 60 * 3600));
                setcookie('username',$row['username'],time() + ( 60 * 60 * 3600));
                header('Location: http://www.google.com');    

            }
            else
            {
                $error_msg = 'enter a valid username and password';
            }
        }
        else
        {
            $error_msg = 'you have to enter username and password to Log In...';
        }
    }
   }
}
?>

Here’s the line 26.

if(mysqli_num_rows($data) == 1)

Answer 1

There is likely an error in your query. For example, an unknown column name or similar issue will let mysqli_query return false (a boolean). I suggest you double check your query’s contents to fix any typo. See http://php.net/manual/en/mysqli.query.php for more details.