NOCYCLE in Postgres - sql

Question

I have a Oracle query with a NOCYCLE clause which I have to translate to Postgres:
SELECT FG_ID,CONNECT_BY_ROOT FG_ID as Parent_ID
FROM FG t
START WITH t.Parent_filter_group_id is null
CONNECT BY NOCYCLE PRIOR t.FILTER_GROUP_ID = t.PARENT_FILTER_GROUP_ID
I have converted this one with the help of the question and answer in
connect_by_root equivalent in postgres
as
with recursive fg_tree as (
select FG_ID,
FG_ID as fg
from FG
where Parent_filter_group_id is null
union all
select c.FG_ID,
p.fg
from FG c join fg_tree p on p.FG_ID = PARENT_FILTER_GROUP_ID
)
select * from fg_tree
order by FG_ID
but in this there is no clause for NOCYCLE if the parent is also one of the children then this query will return error.

Answer 1

You can collect the IDs for each level and then join on the condition that the "current" id is not contained in the path:
with recursive fg_tree as (
select FG_ID,
FG_ID as fg,
array[fg_id] as path
from FG
where Parent_filter_group_id is null
union all
select c.FG_ID,
p.fg,
p.fg||c.fg_id
from FG c
join fg_tree p on p.FG_ID and c.fg_id <> ALL (p.path)
)
select fg_id, fg
from fg_tree
order by filter_group_id

Answer 2

oracle version:
SELECT o.object_id, p.plugin_id AS plugin_id, LEVEL, CONNECT_BY_ISCYCLE "Cycle"
FROM sst_cycle_obj o LEFT JOIN sst_cycle_devplug p ON p.device_id = o.object_id
WHERE CONNECT_BY_ISCYCLE = 1
CONNECT BY NOCYCLE o.object_id = PRIOR p.plugin_id
START WITH o.object_id = 11
create table sst_cycle_obj
(object_id numeric(10))
create table sst_cycle_devplug
(device_id numeric(10)
,plugin_id numeric(10))
insert into sst_cycle_obj (object_id)
(select 11 from dual
union all
select 12 from dual
union all
select 13 from dual)
insert into sst_cycle_devplug (device_id,plugin_id)
(select 11, 12 from dual
union all
select 12, 13 from dual
union all
select 13,11 from dual)
-->NOCYCLE2 CONNECT_BY_ISCYCLE "Cycle" Postgresql version
WITH recursive ncot
AS
(SELECT a.device_id,a.plugin_id,('{'||a.device_id||'}')::numeric[] as PATH, 0 AS cycle1, 1::int as level
FROM ( select o.object_id device_id, p.plugin_id as plugin_id
from sst_cycle_obj o
left join sst_cycle_devplug p on p.device_id=o.object_id
) a
WHERE a.device_id = 11
UNION ALL
SELECT objt.device_id,objt.plugin_id, ncot.path||objt.device_id::numeric as PATH, CASE WHEN objt.plugin_id = any(ncot.path) THEN 1 else 0 END AS cycle1, ncot.level + 1 as level
FROM ( select o.object_id device_id, p.plugin_id as plugin_id
from sst_cycle_obj o
left join sst_cycle_devplug p on p.device_id=o.object_id
) objt
JOIN ncot ON objt.device_id = ncot.plugin_id and objt.device_id <> ALL (ncot.path)
)
SELECT device_id,plugin_id,PATH,cycle1,level
FROM ncot
WHERE cycle1=1
--<