SQL Select with root parent - postgresql

Question

I have a table Members(id, name, parent_id), where parent_id is the parent of the member(it is also a member which can have its parent). For example
id | name | parent_id
----------------------
1 | John | NULL
2 | Smith| 1
3 | Andy | 1
4 | Joe | 2
5 | Rick | 2
6 | Craig| 5
7 | Greg | NULL
8 | Bob | 5
9 | Mike | 8
And I'd like to run statement select from members, and I want to have
id | name | parent_id | root_parent_id
--------------------------------------
1 | John | NULL | NULL
2 | Smith| 1 | 1
3 | Andy | 1 | 1
4 | Joe | 2 | 1
5 | Rick | 2 | 1
6 | Craig| 5 | 1
7 | Greg | NULL | NULL
8 | Bob | 7 | 7
9 | Mike | 8 | 7
I want to find the root_parent_id for all members as deeply as possible. Help me please

Answer 1

with recursive recursive_members as (
select *, id root_id, 1 depth
from members
union all
select r.id, r.name, r.parent_id, m.parent_id, r.depth+ 1
from recursive_members r
join members m on r.root_id = m.id
where m.parent_id notnull
)
select distinct on (id) *
from recursive_members
order by id, depth desc;
id | name | parent_id | root_id | depth
----+-------+-----------+---------+-------
1 | John | | 1 | 1
2 | Smith | 1 | 1 | 2
3 | Andy | 1 | 1 | 2
4 | Joe | 2 | 1 | 3
5 | Rick | 2 | 1 | 3
6 | Craig | 5 | 1 | 4
7 | Greg | | 7 | 1
8 | Bob | 5 | 1 | 4
9 | Mike | 8 | 1 | 5
(9 rows)
Read about recursive WITH queries.