SQL级联查询有关问题

--第一级 select ciid from communityinfor as Community where parent!=0 and parent not in (select ciid from communityinfor )--第二级select ciid from communityinfor where parent in (select ciid from communityinfor as Community where parent!=0 and parent not in (select ciid from communityinfor ))--第三级select ciid from communityinfor where parent in(select ciid from communityinfor where parent in (select ciid from communityinfor as Community where parent!=0 and parent not in (select ciid from communityinfor )))

/*==============================================================*//* Table: communityinfor                                        *//*==============================================================*/create table communityinfor (   ciid                 int                  identity,   levelid              int                  not null,   parent               int                  not null,   communityname        varchar(50)          not null,   constraint pk_communityinfor primary key (ciid))godeclare @currentuser sysnameselect @currentuser = user_name()execute sp_addextendedproperty 'MS_Description',    '小区信息   需要具体到室   页面需要树控件显示出小区的所有信息。 从小区到室。 所有节点的信息   1.CIID ID   2.LevelID    级别信息外键ID[LevelInfor]表的外键。指示该节点所属的级别      4.Parent      父级。例如 1单元，它所属的栋级 是哪个 ？此字段引用自己的主键   5.CommunityName      节点的完整名称。  例如一栋一单元， 或者一栋一单元0101室   ',   'user', @currentuser, 'table', 'communityinfor'go