Oracle Hierarchy to get all children and all parents of each id - sql

Question

I have a table with parent/child ids, and I'm trying to get a full list of all levels of parents AND children for a given id.
Basically, for a given id, go all the way down and all the way up the hierarchy.
I've tried connect by, but maybe a recursive CTE would be better?
select 'abc' as child, null as parent from dual union all
select 'mno' as child, 'abc' as parent from dual union all
select 'def' as child, 'abc' as parent from dual union all
select '123' as child, 'abc' as parent from dual union all
select 'qrs' as child, '123' as parent from dual union all
select '789' as child, 'def' as parent from dual union all
select 'xyz' as child, '123' as parent from dual
Ex:
Child
Parent
abc
null
mno
abc
def
abc
123
abc
qrs
123
789
def
xyz
123
For 123, the desired output:
xyz > 123 > abc
qrs > 123 > abc
For abc, the desired output:
xyz > 123 > abc
789 > def > abc
qrs > 123 > abc
mno > abc
Here's my attempt. It seems kind of hacky with the full_hier being a concatenation + substring of the child & parent paths. Plus, I'm getting additional results that I'm not sure how to filter out (Ex: def > abc is returned though I don't want it as it's captured in 789 > def > abc).
select
connect_by_root child,
substr(sys_connect_by_path(child, '>' ),2) as child_hier
, substr(sys_connect_by_path(parent, '>' ),2) as parent_hier
, case
when parent is null then substr(sys_connect_by_path(child, '>' ),2)
else substr(sys_connect_by_path(child, '>' ),2) || substr(substr(sys_connect_by_path(parent, '>' ),2), instr(substr(sys_connect_by_path(parent, '>' ),2),'>',1,1))
end as full_hier
, level
from
(
select 'abc' as child, null as parent from dual union all
select 'mno' as child, 'abc' as parent from dual union all
select 'def' as child, 'abc' as parent from dual union all
select '123' as child, 'abc' as parent from dual union all
select 'qrs' as child, '123' as parent from dual union all
select '789' as child, 'def' as parent from dual union all
select 'xyz' as child, '123' as parent from dual
) table_name
where 1=1
--and connect_by_isleaf = 1
--and connect_by_root child in ('123')
and child = 'abc'
connect by child = prior parent
--connect_by prior parent = child
Thanks for taking a look, I appreciate it!

Answer 1

Another method.
This time via recursive CTE's.
with cte_init (base) as (
select '123' as base
from dual
),
rcte_hierarchy_down (base, lvl, child, parent) as (
select
child as base
, 0 as lvl
, child
, parent
from test_hierarchy
where child in (select base from cte_init)
union all
select
cte.base
, cte.lvl-1
, t.child
, t.parent
from rcte_hierarchy_down cte
join test_hierarchy t
on t.child = cte.parent
),
rcte_hierarchy_up (lvl, child, parent, path) as (
select
1 as lvl
, child
, parent
, child||'>'||parent as path
from test_hierarchy h
where parent in (select child
from rcte_hierarchy_down
where parent is null)
union all
select
cte.lvl+1
, t.child
, t.parent
, t.child||'>'||cte.path
from rcte_hierarchy_up cte
join test_hierarchy t
on t.parent = cte.child
)
select distinct h.path
from rcte_hierarchy_up h
join cte_init i on h.path like '%'||i.base||'%'
and not exists (
select 1
from test_hierarchy t
where t.parent = h.child
)
PATH
qrs>123>abc
xyz>123>abc
Demo on db<>fiddle here

Answer 2

If I understand correctly, given any id (as an input - below I use a bind variable in the query), you need to find all its leaf descendants, and then for each such leaf, show the full path from leaf to the root of the hierarchy.
One way to do that is to traverse the hierarchy twice: first start from the given id and find all its leaf descendants, then traverse in the opposite direction to find all the "full paths".
While this may look (marginally) more elegant, it will be significantly less efficient. The better approach is along the lines you were trying already.
Below I use the with clause (and give column names in the subquery declaration - that is only supported since Oracle 11.2, if your version is 11.1 you will need to move the aliases into the select clauses as you were doing in your attempt).
with
table_name (child, parent) as (
select 'abc', null from dual union all
select 'mno', 'abc' from dual union all
select 'def', 'abc' from dual union all
select '123', 'abc' from dual union all
select 'qrs', '123' from dual union all
select '789', 'def' from dual union all
select 'xyz', '123' from dual
)
, a (ancestor_path) as (
select sys_connect_by_path(child, '>')
from table_name
where connect_by_isleaf = 1
start with child = :i_child
connect by child = prior parent
)
, d (descendant_path) as (
select substr(sys_connect_by_path(child, '>'), 2)
from table_name
where connect_by_isleaf = 1
start with parent = :i_child
connect by parent = prior child
)
select d.descendant_path || a.ancestor_path as full_path
from d cross join a
;

Answer 3

Here's a method that first descends down the tree to get the root parent(s) from the chosen one.
Then uses those roots to climb back up.
The resulting paths are then filtered on the chosen child.
And what remains are those where the final child isn't a parent.
create table test_hierarchy (
child varchar(3),
parent varchar(3),
primary key (child)
);
insert into test_hierarchy (child, parent)
select 'abc' as child, null as parent from dual union all
select 'mno' as child, 'abc' as parent from dual union all
select 'def' as child, 'abc' as parent from dual union all
select '123' as child, 'abc' as parent from dual union all
select 'qrs' as child, '123' as parent from dual union all
select '789' as child, 'def' as parent from dual union all
select 'xyz' as child, '123' as parent from dual;
with cte (base) as (
select '123' from dual
)
select *
from
(
select
sys_connect_by_path(child,'>') as path
, cte.base
, level
, connect_by_root child as child
from test_hierarchy
cross join cte
where child in (
select connect_by_root child
from test_hierarchy
where child in (select base from cte)
and connect_by_root parent is null
connect by prior child = parent
)
connect by prior parent = child
) q
where path like '%'||base||'%'
and not exists (
select 1
from test_hierarchy t
where t.parent = q.child
)
PATH
BASE
LEVEL
CHILD
>qrs>123>abc
123
3
qrs
>xyz>123>abc
123
3
xyz
Demo on db<>fiddle here