有没有在connect by oracle with nocycle中添加一个循环行？

Question

就像当循环发生在顶层节点（根节点直接连接回根节点）时 Oracle 继续遵循循环之外的路径一样，有没有办法在循环之间做同样的事情。就像我有一些像下面这样的数据

create table t1 ( c1 varchar2(2), c2 varchar2(2));
insert into t1 values ('A', 'B');
insert into t1 values ('B', 'C');
insert into t1 values ('C', '**A**');

并执行以下查询：

select * from (
select distinct 
  connect_by_root c1 as c3,
  c1,
  c2
from t1 
connect by nocycle c1 = prior c2
) where c3='A';

它会给我这个结果

c3  c1  c2
A   A   B
A   B   C
**A**   **C**   **A**

它给了我根循环值。但是如果我有如下数据。

create table t2 ( c1 varchar2(2), c2 varchar2(2));
insert into t2 values ('A', 'B');
insert into t2 values ('B', 'C');
insert into t2 values ('C', '**B**');


select * from (
select distinct 
  connect_by_root c1 as c3,
  c1,
  c2
from t2 
connect by nocycle c1 = prior c2
) where c3='A';

这给了我

c3  c1  c2
A   A   B
A   B   C

但我还需要第三排，即 A C B。所以想知道这是否可以做到？

Answer 1

您可以使用递归子查询分解子句：

WITH rsqfc ( c3, c1, c2 ) AS (
  SELECT c1, c1, c2 
  FROM   t2
  WHERE  c1 = 'A'
UNION ALL
  SELECT r.c3, t.c1, t.c2
  FROM   t2 t
         INNER JOIN rsqfc r
         ON ( t.c1 = r.c2 )
)
CYCLE c1, c2 SET is_cycle TO 1 DEFAULT 0
SELECT c3, c1, c2
FROM   rsqfc
WHERE  is_cycle = 0;

其中，对于您的示例数据：

create table t2 ( c1, c2 ) AS
SELECT 'A', 'B' FROM DUAL UNION ALL
SELECT 'B', 'C' FROM DUAL UNION ALL
SELECT 'C', 'B' FROM DUAL;

输出：

C3 | C1 | C2
:- | :- | :-
A  | A  | B 
A  | B  | C 
A  | C  | B

db<>fiddle here

有没有在connect by oracle with nocycle中添加一个循环行？

Is there any to add one loop row in connect by oracle with nocycle?

oracle

connect-by