CodeIgniter查询构建

我不明白为什么这个查询只获取1行，但必须有34000行。生成时没有错误$fromDate='2015-10-01'，$toDate='2015-10-31'$supervisorIdArray是一个扁平数组。

        $this->db->select('production.supervisor_id,production.employee_id,production.operation_id, SUM(production.quantity) as quantity,production_operation.operation_id,production_operation.rate');
        $this->db->from('production');
        $this->db->join('production_operation','production_operation.operation_id = production.operation_id', 'left');
        $this->db->where('production.production_date >=',$fromDate);
        $this->db->where('production.production_date <=',$toDate);
        $this->db->where_in('production.supervisor_id',$supervisorIdArray); 
        $this->db->order_by('production.supervisor_id','ASC');
        $this->db->order_by('production.employee_id','ASC');
        $this->db->order_by('production.operation_id','ASC');                    
        $query = $this->db->get();
        $Rows = $query->num_rows();