下面有两个表子类别tblsub_idsub_titlesub_parent_id1Forrent02Car13Motorcycle14ForSale05Boat4项目列表item_idsub_id122233415265汽车和摩托车在出租子类别下，船在待售子类别下。因此，结果应该是这样的:ForRent(5)-Car(3)-Motorcycle(1)ForSale(1)-Boat(1)下面是我的查询:SELECTcount(*)asitemcount,sub_parent_idfromsubcategorytblLEFTJOINitemtblONsubcategorytbl.sub_i