我想先加入subcategory和subling，应该是joinmastercategory的子查询$users=DB::table('mastercategory')->join('subcategory','mastercategory.idcategory','=','subcategory.idcategory_mastercategory')->join('subling','subcategory.idsubcategory','=','subling.idsubcategory_subcategory')->select('mastercategory.*','subca