Why Does `mysqli_num_rows()` Return 'boolean given' After Using HTML Purifier and `mysqli_query()`?

mysqli_num_rows() Expects Parameter 1 to be mysqli_Result, Boolean Given in PHP & MySQL

Error Message

When using HTML Purifier to filter user input and executing a query using mysqli_query(), you may encounter the error:

mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given

This error occurs when mysqli_num_rows() is called with a boolean value instead of an mysqli_result object.

Solution

The root cause of the error is an issue in the SQL query. In the given code, the query:

SELECT users.*, profile.*
                                 FROM users
                                 INNER JOIN contact_info
                                 ON contact_info.user_id = users.user_id
                                 WHERE users.user_id=3");

contains an error: there is no JOIN with the profile table anywhere in the query. To fix this, you need to include the correct JOIN statement in the query.

The corrected query:

SELECT users.*, profile.*
                                 FROM users
                                 INNER JOIN profile
                                 ON contact_info.user_id = users.user_id
                                 WHERE users.user_id=3");

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