Inner Join user tables to select users with roles

I am trying to view a list of users (who are music artists) with the following function.

function show_authors($ltr) {
    global $wpdb;
    $querystr = "SELECT $wpdb-users.* FROM $wpdb-users WHERE $wpdb-users.display_name LIKE '$ltr%' ORDER BY $wpdb-users.display_name";

/**
    $querystr = "
    SELECT      *
    FROM        $wpdb-users
    INNER JOIN  $wpdb-usermeta.meta_value
                ON $wpdb-users.user_id = $wpdb-usermeta.user_id
                AND $wpdb-usermeta.meta_key = 'wp_capabilities'
                AND $wpdb-usermeta.meta_value = %artist%
    WHERE       $wpdb-users.display_name LIKE '$ltr%' 
            AND $wpdb-usermeta.meta_key = 'wp_capabilities' 
                    AND $wpdb-usermeta.meta_value LIKE '%artist%'
    ORDER BY    $wpdb-users.display_name ASC
    ";
**/

    $users = $wpdb-get_col($querystr);
    echo "ul style=\"list-style-type: none;\"";
        foreach($users as $user) {
          $user = get_userdata($user);
          $post_count = get_usernumposts($user-ID);
           echo 'lii class="fa fa-user"/i a href="' . get_author_posts_url($user-ID, $user-user_nicename) . '" ' . $user-first_name . ' ' . $user-last_name . '/a ('. $post_count .' songs)/li';
    }
    echo "/ul";
}

I tried inner join the usermeta table so that I can select the necessary users with the meta_key named wp_capabilities which has the name of the user role in the meta_value field.

The shown code works fine. When I try to use the commented out query, the result is empty. What I might be doing wrong? Or is there any efficient or better way to achieve this?