Comments on: Oracle 11gR2 – alternative for CONNECT_BY_ISLEAF function for Recursive Subquery Factoring (dedicated to Anton)

By: JÃ¼rgen Sieben

JÃ¼rgen Sieben — Sun, 25 Dec 2011 09:20:21 +0000

I guess what you’re looking for in first place could be achieved more securely with a scalar subquery like so:

with hierarchie (lvl, ename, empno, is_leaf) as (
select 1 lvl, ename, empno,
(select decode(count(*), 0, 1, 0)
from emp
where mgr = m.empno) is_leaf
from emp m
where mgr is null
union all
select h.lvl + 1, e.ename, e.empno,
(select decode(count(*), 0, 1, 0)
from emp
where mgr = e.empno) is_leaf
from hierarchie h, emp e
where h.empno = e.mgr)
search depth first by ename set sort_seq
select lvl, ename, is_leaf
from hierarchy;
To my understanding, this is somewhat easier to use. Whether this on the other hand is still performant is another question.
Best regards,
JÃ¼rgen

By: Mette Stephansen

Mette Stephansen — Mon, 13 Dec 2010 14:34:09 +0000

Hi there.

Very nice post

How would I get the is_leaf if the ordering is not by depth, but by breadth ?

Regards
Mette

By: Lucas

Lucas — Wed, 18 Nov 2009 15:06:21 +0000

Is what you are asking for just the root node for every leaf-node – it seems that way at least. Of course it is easy to add the root to every node returned from the query and then filter on is_leaf = 1. Something like:

WITH
each_level (empid, name, mgrid, lev, root) AS
(
SELECT empno, ename, mgr , 1, ename
FROM emp
WHERE mgr is null
UNION ALL
SELECT empno, ename, mgr, lev+1, root
FROM each_level r, emp e
WHERE r.empid = e.mgr
)
SEARCH DEPTH FIRST BY mgrid SET seq
, leafNodes as
( select e.*
from each_level e
where case
when (lev – lead(lev) over (order by seq)) < 0
then 0
else 1
end = 1
)
select ename
, root top_manager
from leafNodes

Or are you looking for something else?

By: Anton Scheffer

Anton Scheffer — Mon, 16 Nov 2009 15:27:30 +0000

Of course I’m satisfied! But can you use it to find the topmanager from every employee? Something like:

select emp.empid
, emp.name
, ( select mgr.name
from emp mgr
where connect_by_isleaf = 1
connect by mgr.empid = prior mgr.mgr
start with mgr.empid = emp.mgr
) top_manager
from emp emp

By: Rob van Wijk

Rob van Wijk — Sat, 14 Nov 2009 09:51:21 +0000

Hi Lucas,

Brilliant idea! I just finished a session telling my audience there is no alternative for connect_by_isleaf. I’ll have to revise that statement …
By the way, cycle detection is still different from the connect-by syntax. Maybe you can even call it wrong but that’s subjective. And did you compare execution plans and performance? If you do, you’ll stick with connect-by. At least for some cases.

Regards,
Rob.