Haal de lege records op met SQL

Waarom tellen niet gewoon hele records?

public function getBoxOpenings($boxes, $from_date, $to_date){
$query = $this->db->select('box_id, COUNT(*) AS Openings')
    ->from('mc_boxes_has_openings')
    ->where_in('box_id', $boxes)
    ->where('actiontime >=', $from_date)
    ->where('actiontime <=', $to_date)
    ->group_by('box_id')
    ->get();
$data = $query->result_array();
return $data;
}

Hoewel ik je group_by-clausule niet begrijp...