Answer Posted / gvmahesh

NOCYCLE keyword is default in sequences.

CYCLE :If we want use cycle keyword first we check the table
having primary key or not.If there is no primary key we
absolutely use the CYCLE keyword.

In hierarchical structure,the descendant act as a
ancestor,is called CYCLE.

For eliminating ancestor descendant problem we use NOCYCLE
KEYWORD.

for example we take the EMP table

In EMP table the MGR column has a NULL managerial number.In
that column we insert some of the empno.Then ancestor
descendant problem occur.

select * from emp;

update emp set mgr=7566 where mgr is null;

Then we write a hierarchical query

select empno,ename,sal,mgr from emp
start with ename='KING'
connect by prior empno=mgr;

we execute this query it shows an error

ERROR:
ORA-01436: CONNECT BY loop in user data.

in this situation also we want to see the data through
NOCYCLE keyword.

select empno,ename,sal,mgr from emp
start with ename='KING'
connect by NOCYCLE prior empno=mgr;

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