SQL & PL/SQL

HI ...you can use connect_by_root to find all the id's IN a hierarchy ...to find the one's NOT IN hirarachy should not be a problem from there ... any sample data ???

What is your database version?
How about providing some create table statements and example data (insert statements) for us?
How about showing what output you would expect from that example data?

Hi,

Welcome to the forum!

It might be more efficient to do a CONNECT BY query, and find the nodes that are leaves at the top level:

SELECT	*
FROM	table_x
WHERE	CONNECT_BY_ISLEAF	= 1
AND	LEVEL			= 1
START WITH	parent_id	IS NULL
CONNECT BY	parent_id	= PRIOR id
	AND	LEVEL		<= 2	-- For efficiency
;

Whenever you have a problem, post a little sample data (CREATE TABLE and INSERT statements) and the results you want from that data.
It helps to mention which version of Oracle you're using, especially when asking about CONNECT BY queries, where every version since Oracle 7 has had significant changes.

Or something like this...

SQL> ed
Wrote file afiedt.buf

  1  with t as (select null as mgr, 1 as emp_id, 'Chairman' as position from dual union all
  2             select 1, 2, 'Vice Chairman' from dual union all
  3             select 2, 3, 'Company Director' from dual union all
  4             select 3, 4, 'Sales Manager' from dual union all
  5             select 3, 5, 'Technology Manager' from dual union all
  6             select 3, 6, 'HR Manager' from dual union all
  7             select 4, 7, 'Sales Rep' from dual union all
  8             select 4, 8, 'Sales Rep' from dual union all
  9             select 4, 9, 'Sales Rep' from dual union all
 10             select 10, 10, 'Dodgy Contractor' from dual union all
 11             select 5, 11, 'Software Developer' from dual union all
 12             select 5, 12, 'Software Developer' from dual union all
 13             select 5, 13, 'Network Specialist' from dual union all
 14             select 5, 14, 'Communications Implementer' from dual union all
 15             select 6, 15, 'Rectruitment Agent' from dual union all
 16             select 6, 16, 'Job Marketing Agent' from dual union all
 17             select 6, 17, 'Job Marketing Assistant' from dual)
 18  --
 19  -- END OF TEST DATA
 20  --
 21  select emp_id from t
 22  minus
 23  select emp_id
 24  from   t
 25  connect by mgr = prior emp_id
 26* start with mgr is null
SQL> /

    EMP_ID
----------
        10

SQL>

... but it does depend what the data looks like and what exactly you are trying to achieve.

TRY THIS

SELECT 
	EMPNO 
FROM 
	SCOTT.EMP 
WHERE 
	EMPNO NOT IN 
	(
		SELECT 
			EMPNO 
		FROM 
			SCOTT.EMP 
		CONNECT BY PRIOR 
			EMPNO=MGR 
		START WITH MGR = 7566
	)