Deactivation Hook does not remove database

function my_plugin_remove_database()
{
    global $wpdb;
    $db_table_name = $wpdb->prefix . 'sandbox';  // table name
    $sql = "DROP TABLE IF EXISTS $db_table_name";
    $rslt=$wpdb->query($sql);
}

register_deactivation_hook( __FILE__, 'my_plugin_remove_database' );