遇到个业务场景，分层级显示数据库的表，该表主键为bas_wrapper_uuid，并且有层级关系字段pre_bas_wrapper_uuid，该字段与某条数据的主键关联。标识上一层级的数据，用level来标识级数，

  select level as label_Num,
       bw.bas_wrapper_uuid,
       bw.wrapper_code,
       bw.wrapper_name,
       bw.pre_bas_wrapper_uuid,
       bw.wrapper_type
  from bas_wrapper bw
  where 0 = 0
 start with bw.pre_bas_wrapper_uuid is null and bw.status='Active' and bw.wrapper_type in('PACKAGE_MATERIAL','PACKAGE_GROUP')
connect by prior bw.bas_wrapper_uuid = bw.pre_bas_wrapper_uuid
order by label_Num

其中level为层级显示的排序，
start whit 后接条件
connect by prior 自关联字段
order by 排序显示，也可以在where 下面加上显示分组之后的查询条件，进行对应的查询