php – Altering common db connection to $wpdb

I’m engaged on a wordpress web site, and began implanting a CRUD database. I coded out an instance that works completely on my localhost. Nevertheless, I’m working with file mangaer in cpanel, and am having problem with altering the common database question to a one that’s integrated with $wpdb. I’ve tried to make use of $wpdb->get_results(), however I get the identical error. Any assist can be significantly appreciated.

Right here is my code:

  // CONNECTION TO DATABASE
    $question = "SELECT * FROM college students";
    $query_results = mysqli_query($wpdb->dbh, $question) or die(mysqli_error($wpdb->dbh));

    if(mysqli_num_rows($query_results) > 0) 
    {
        foreach($query_run as $scholar)
        {
            ?>
            echo '
                <type id="saveStudent">
                    <tr>' 
                        echo '<td>'<?php $student->id; ?> echo '</td>';
                        echo '<td>'<?php $student->first_name; ?> echo '</td>';
                        echo '<td>'<?php $student->last_name; ?> echo '</td>';
                        echo '<button sort="button" class="btn btn-danger">Delete Scholar</button>'

            echo '</tr>';
            
            <?php
        }
    }
    ?>

EDIT: The error message I get is Warning: mysqli_query() expects parameter 1 to be mysqli, null given