使用SQL语句查询形成环路的关系数据

WITH ROOT_NODE (
parent)
AS
(SELECT   parent
FROM   TABLE1
WHERE   parent LIKE 'grandpa' || '%'), --若已知大概范围
FIND_CALL_RST (
SVC,
parent,
child,
CALL_LEVEL,
VAL)
AS
(SELECT   parent AS SVC,
parent,
child,
1 AS CALL_LEVEL,
CAST (
parent || '->' || child AS VARCHAR (1000))
VAL
FROM   TABLE1
WHERE   parent IN (SELECT   parent FROM ROOT_NODE)
UNION ALL
SELECT   VT.SVC,
T.parent,
T.child,
VT.CALL_LEVEL + 1,
VT.VAL || '->' || T.child AS VAL
FROM   FIND_CALL_RST VT, TABLE1 T
WHERE   T.parent = VT.child AND CALL_LEVEL < 20)
SELECT   CALL_LEVEL, A.VAL
FROM   FIND_CALL_RST A
WHERE   A.CALL_LEVEL > 19