Why does `mysqli_num_rows()` return 'expects parameter 1 to be mysqli_result, boolean given'?

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

Error Analysis

The error message "mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given" arises when trying to use the mysqli_num_rows() function on a boolean value instead of a valid MySQL result set (mysqli_result).

Source of the Error

In the provided code, the error occurs on line 22:

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

Debugging the Issue

The variable $dbc is assigned on line 13 using the mysqli_query() function. However, examining the query reveals an error:

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

The query attempts to join the "users" and "profile" tables using an "INNER JOIN," but there is no join condition between "profile" and any other table. As a result, the query returns false (boolean false).

Resolution

To resolve the error, the query must be corrected to include a proper join condition. Here is the corrected query:

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

With this correction, the query will return a valid MySQL result set, allowing mysqli_num_rows() to operate correctly.

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