Hello,
I have a table in my database with multiple, independent linked lists. I would like to have a query that returns an entire linked list given a node (the node could be anywhere within the list).
I found on the web an example of how to use CTEs to do this:
I'll repeat the gist of it here:
CREATE TABLE department ( id INTEGER PRIMARY KEY, -- department ID parent_department INTEGER REFERENCES department, -- upper department ID name TEXT -- department name
);
INSERT INTO department (id, parent_department, "name")
VALUES (0, NULL, 'ROOT'), (1, 0, 'A'), (2, 1, 'B'), (3, 2, 'C'), (4, 2, 'D'), (5, 0, 'E'), (6, 4, 'F'), (7, 5, 'G');
-- department structure represented here is as follows:
--
-- ROOT-+->A-+->B-+->C
-- | |
-- | +->D-+->F
-- +->E-+->G
To extract all departments under A, you can use the following recursive query:
WITH RECURSIVE subdepartment AS
( -- non-recursive term SELECT * FROM department WHERE name = 'A'
UNION ALL
-- recursive term SELECT d.* FROM department AS d JOIN subdepartment AS sd ON (d.parent_department = sd.id)
)
SELECT *
FROM subdepartment
ORDER BY name;
My database contains multiple, independent structures like the one given above. So, I can modify the above with:
insert into department (id, parent_department, name) values (8, NULL, 'Z'), (9, 8, 'Y');
I need a bidirectional query and since I'm quite new to CTE, I'm not sure how to modify the query to get parent departments as well as subdepartments... Thus, if I give the query any node in a linked list, I'd like the entire tree returned.
e.g. If I give the query 'A', I'd like it to return the ROOT, A, B, C, D, E, F, G tree. If I give the query 'Y', I'd like it to return the Z, Y tree.
I hope I made sense...
Thanks!
Mark