PHP MySQL mysqli num rows expects parameter 1 to be mysqli result boolean given

Question

I'm trying to Integrate HTML Purifier http://htmlpurifier.org/ to filter my user submitted data and I was wondering how can I fix this problem as I get the following error:-

on line 22: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given

line 22 is.

if (mysqli_num_rows($dbc) == 0) {

Here is the php code.

if (isset($_POST['submitted'])) { // Handle the form. 

  require_once '../../htmlpurifier/library/HTMLPurifier.auto.php'; 

$config = HTMLPurifier_Config::createDefault(); 
$config->set('Core.Encoding', 'UTF-8'); // replace with your encoding 
$config->set('HTML.Doctype', 'XHTML 1.0 Strict'); // replace with your doctype 
$purifier = new HTMLPurifier($config); 

$mysqli = mysqli_connect("localhost", "root", "", "sitename"); 
$dbc = mysqli_query($mysqli,"SELECT users.*, profile.* 
                                                    FROM users 
                                                    INNER JOIN contact_info ON contact_info.user_id = users.user_id  WHERE users.user_id=3");

$about_me = mysqli_real_escape_string($mysqli, $purifier->purify($_POST['about_me'])); $interests = mysqli_real_escape_string($mysqli, $purifier->purify($_POST['interests'])); 

if (mysqli_num_rows($dbc) == 0) { 
            $mysqli = mysqli_connect("localhost", "root", "", "sitename"); 
            $dbc = mysqli_query($mysqli,"INSERT INTO profile (user_id, about_me, interests) 
                                                                  VALUES ('$user_id', '$about_me', '$interests')"); 
} 


if ($dbc == TRUE) { 
            $dbc = mysqli_query($mysqli,"UPDATE profile 
                                                                  SET about_me = '$about_me', interests = '$interests' 
                                                                  WHERE user_id = '$user_id'"); 

echo '<p class="changes-saved">Your changes have been saved!</p>'; 

} 

if (!$dbc) {

                  // There was an error...do something about it here... 
                  print mysqli_error($mysqli); 
                return; 
} 

}

Answer 1

Your query seems to have an ERROR in it due to the $dbc returning false:-

SELECT users.*, profile.* --You do not join with profile anywhere. 
                                                FROM users 
                                                INNER JOIN contact_info 
                                                ON contact_info.user_id = users.user_id 
                                                WHERE users.user_id=3");

The query either returns no rows or is erroneous, thus FALSE is returned. Alter that to:-
 

if (!$dbc || mysqli_num_rows($dbc) == 0)

Mysqli_num_rows:

Return Values

Returns TRUE on success or FALSE on failure. For SELECT, SHOW, DESCRIBE or EXPLAIN mysqli_query() will return a result object.