Why Does `mysqli_num_rows()` Return a Boolean Instead of a `mysqli_result` Object?

PHP & MySQL: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given

Problem

When integrating HTML Purifier into a PHP script, an error occurs in line 22: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given. The error is triggered when attempting to check the number of rows returned by a MySQL query.

Solution

The error is caused by an incorrect SQL query in line 22, which is:

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

The error is: "You do not join with profile anywhere." This means that the query is trying to join the users and profile tables on the user_id column, but the profile table is not included in the FROM clause.

To fix the issue, the profile table needs to be included in the FROM clause, like so:

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

With this change, the query will correctly join the users and profile tables and return the desired results.

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