oracle树形结构相关查询

查询最顶层元素

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select * from basic_type t WHERE NOT exists(select 'x' from basic_type t1,basic_type t2 where t1.id=t2.parentid and t1.id= t.parentid)

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查询id为'asdfas'的属于顶层ID为4的第几级

?select * from (select LEVEL,id,parentid,name from basic_type START WITH id='4'?
?? CONNECT BY PRIOR id=parentid) where id= 'asdfas'