public function buildGroupBy($columns, $limit)
{
if (empty($columns)) {
return '';
}
if (is_string($limit) && ctype_digit($limit) || is_int($limit) && $limit >= 0) {
$limitSql = ' ' . $limit;
} else {
$limitSql = '';
}
return 'GROUP' . $limitSql . ' BY ' . $this->buildColumns($columns);
}