Oracle 分层问题（查找继兄弟姐妹）

Question

我正在解决一个问题，从任何 'leaf' 或 child 开始，我可以找到 child 的兄弟姐妹和继兄弟姐妹。举个更好的例子，如果parentA有两个children，和parentB共用一个child，而parentB有两个children，一个与 parent A 共享，一个与 parent C 共享，parent c 还有两个 children 不与 parent B 共享，我如何报告所有 children？我试过使用递归和分层查询，但似乎无法正确使用。以下是 table 结构和值以及我迄今为止的尝试。

create table bw_parents(
parent_id char(1) primary key);


create table bw_children(
child_id number(2),
parent_id char(1),
constraint parent_id_fk FOREIGN KEY (parent_id) references bw_parents
);

insert into bw_parents values('A');

insert into bw_parents values('B');

insert into bw_parents values('C');

insert into bw_parents values('D');

insert into bw_parents values('E');

insert into bw_children values(1,'A');

insert into bw_children values(2,'A');

insert into bw_children values(2,'B');

insert into bw_children values(3,'B');

insert into bw_children values(3,'C');

insert into bw_children values(4,'C');

insert into bw_children values(5,'C');

insert into bw_children values(6,'D');

insert into bw_children values(7,'D');

insert into bw_children values(8,'E');

--hierarchical attempt
select A.parent_id, B.child_id, level
from bw_parents A
join bw_children B ON A.parent_id = B.parent_id
start with A.parent_id = 'B'
connect by nocycle prior B.parent_id = B.parent_id

--recursive with
with r as(
select parent_id, null as child_id
from bw_parents
union all 
select A.parent_id parent_id, B.child_id child_id
from bw_parents A
join bw_children B ON A.parent_id = B.parent_id)

select *
from r
where parent_id = 'B';

Answer 1

这是一个从给定父级开始的简单（但可能不是很高效）解决方案：

select     distinct child_id
from       bw_children
start with parent_id = 'A'
connect by nocycle (mod(level, 2) = 0 and child_id  = prior child_id ) or 
                   (mod(level, 2) = 1 and parent_id = prior parent_id)
;

如果必须以child_id开头，那么在connect by条件下，mod(level, 2)的值必须切换0和1；其余不变

Oracle 分层问题（查找继兄弟姐妹）

Oracle Hierarchical Question (Find step siblings)

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