How to write a query(may be a recursive one) to fetch parent-child hierarchy in Postgresql 8.4? - postgresql

Question

I have a parent child hierarchy that is depicted as in the picture. There is one head office at the top which acts as the parent branch. The other nodes are child branches.
There can be any number of Regional zones and any number of divisional zones can be added to a Regional zone. Similarly, any number of child branches can be added to a divisional zone. Here, User login is provided at all the levels and there I'm facing a difficulty in showing only the branches that is child to the currently logged in users branch. The data base that I'm using is 'Postgresql8.4'. By Googling I found that recursion can be done. But quite frankly I didn't understand the steps followed in most of them. So can someone please help me in solving this piece of puzzle with explanation on the steps followed?
User Table
============
usr_id; //Unique id of user
usr_branch_id; //Id from the branch table
Branch Table
============
branch_id; //Unique id of branch
branch_text_id;
branch_name;
branch_parent;

Answer 1

you would want something like:
WITH RECURSIVE branch_tree AS (
select branch_id, branch_text_id, branch_name, branch_parent,
branch_id::text as path
from branch
where branch_parent is null
union all
select b.branch_id, b.branc_text_id, b.branch_name, b.branch_parent,
t.path || ',' || b.branch_id::text
FROM branch b
JOIN branch_tree t ON b.parent_id = t.branch_id
)
SELECT * FROM branch_tree ORDER BY string_to_array(path, ',')::int[];