failed to get value from database using shortcode exec PHP

i have created the following PHP code

<?php

global $wpdb;

$myrows = $myrows = $wpdb->get_results("SELECT um.meta_value FROM wp_users u, wp_usermeta um
where u.id = um.user_id and um.meta_key='twitter' and u.user_login='soulartist'");

return str_replace("@","",$myrows);

?>

and when i hit the ‘test’ button, it shows messagebox with
“[return_twitter]=”””

when i run the query on phpmyadmin, it returns a single value “@yuliusshandy”

where did i go wrong ?

thanks !

https://wordpress.org/plugins/shortcode-exec-php/