protected function prepareColumns($columns)
    {
        $prefix = DataQuery::applyRelationPrefix($this->relation);
        $table = DataObject::getSchema()->tableForField($this->model, current($columns));
        $fullTable = $prefix . $table;
        $columns = array_map(function ($col) use ($fullTable) {
            return "\"{$fullTable}\".\"{$col}\"";
        }, $columns);
        return implode(',', $columns);
    }