group + count 統計出來的結果不準確

最近用ThinkPHP框架做項目的時候，發現如果同時使用group和count，查詢出來的結果怪怪的，特此記錄，並揪出原因。

出問題的語句：

                 

                                          $count=$plan->table($this->prex."buy_plan as bp")
						->join($this->prex."buy_plan_detail as bpd on bp.plan_id=bpd.plan_id")
						->join($this->prex."ck_materiel as ck on bpd.materiel_id=ck.materiel_id")
						->join($this->prex."ck_materiel_category as ck_m_c on ck.cat_id=ck_m_c.cat_id")
						->join("left join ".$this->prex."buy_supply as bs on bs.supply_id=bpd.supply_id")
						->join("left join ".$this->prex."ck_size as size on ck.size_id=size.size_id")
						->field("ck_m_c.cat_name,bp.*,ck.materiel_desc,bp.total_money,bpd.buy_num,bpd.price,bpd.transport_price,bpd.total_money as bpd_total_money,bpd.get_time,ck.unit,ck.materiel_name,size.size_name,bs.company_name")
						->where($condition)
						->group("bp.plan_id")->count();

如上，在查詢語句中同時使用了group()方法和count()方法。這樣查到的結果並不是分組的數量，而是組成分組的所有記錄條數。

要解決，上面這個問題，需要先用select()將分組查詢出來，然後再用php的count()方法統計分組的數量。所以，將代碼修改如下。

                                          $total=$plan->table($this->prex."buy_plan as bp")
						->join($this->prex."buy_plan_detail as bpd on bp.plan_id=bpd.plan_id")
						->join($this->prex."ck_materiel as ck on bpd.materiel_id=ck.materiel_id")
						->join($this->prex."ck_materiel_category as ck_m_c on ck.cat_id=ck_m_c.cat_id")
						->join("left join ".$this->prex."buy_supply as bs on bs.supply_id=bpd.supply_id")
						->join("left join ".$this->prex."ck_size as size on ck.size_id=size.size_id")
						->field("ck_m_c.cat_name,bp.*,ck.materiel_desc,bp.total_money,bpd.buy_num,bpd.price,bpd.transport_price,bpd.total_money as bpd_total_money,bpd.get_time,ck.unit,ck.materiel_name,size.size_name,bs.company_name")
						->where($condition)
						->group("bp.plan_id")->select();
$num=count($total);