Recursive query to get desired resultset - postgresql

Question

I have three tables: Superobject, object_master and object_child.
SuperObject contains superobj_id and obj_id. obj_master contains all the details about the object.
Object_child has two columns: obj_id and child_id. It contains object and its child. A child can also have a subchild. So, an object can have multiple childs.
SuperObject Table object_child table
sobj1 obj1 obj1 ch_obj1
sobj1 obj2 obj1 ch_obj2
sobj1 obj3 ch_obj1 ch_obj3
I want resultset in format:
obj1 ch_obj1
obj1 ch_obj2
obj1 ch_obj3
obj2 ------
obj2 ------
obj3 ------
I am using the following query:
with recursive objects as (
select objectid
from object_masster
where objectid in (obj1, obj2, obj3)
union
select a.child_id
from object_child a a join objects b on a.objectid = b.objectid
)
select * from objects
It is returning me all the children for the above objects but not in the desired format.

Answer 1

The trick with recursive queries is that you need to store all of the data in the resultset of the seed bit and recursive bit of the union so you can have it to: A) perform the next lookup, B) display whatever you need when you select on the recursive CTE you've built.
So, for your requirements, we need to store the root node (the first objectid you are selecting from your master table), and then parent and child as we recursively select.
Also, because you want that root node to make it through to the end of all the recursive lookup, you need to keep selecting that through in your recursive bit of the union.
This will look something like:
WITH RECURSIVE objects AS (
SELECT objectid AS root, CAST(NULL AS VARCHAR(10)) AS parent, objectid AS child
FROM object_master
WHERE objectid IN (obj1, obj2, obj3)
UNION
SELECT b.root AS root, b.child AS parent, a.child_id AS child
FROM object_child a
INNER JOIN objects b
ON a.objectid = b.child
)
SELECT root, child FROM objects