PostgreSQL get parent categories from table

Question

I have the table as like below.

CREATE TABLE my.categories (id bigint, parent_id bigint, name varchar(128));

INSERT INTO my.categories (id, parent_id, name)         


        

Answer 1

If I get you, this is what you need.

First, with the folowing query you can get all the parent ids:

WITH RECURSIVE t(id, parentlist) AS (
  SELECT id, ARRAY[]::bigint[] FROM my.categories WHERE parent_id IS NULL
  UNION
  SELECT my.categories.id, my.categories.parent_id || t.parentlist
    FROM my.categories 
    JOIN t ON categories.parent_id = t.id
) SELECT * FROM t
-- outputs:
-- id  | parentlist
-- ----+------------
-- 1   | {}
-- 2   | {1}
-- 3   | {1}
-- 4   | {2,1}
-- 5   | {2,1}
-- 6   | {3,1}

If you want to get a record of the parents of one id you just need to change the query like:

WITH RECURSIVE t(id, parentlist) AS (
  SELECT id, ARRAY[]::bigint[] FROM my.categories WHERE parent_id IS NULL
  UNION
  SELECT my.categories.id, my.categories.parent_id || t.parentlist
    FROM my.categories 
    JOIN t ON categories.parent_id = t.id
) SELECT unnest(parentlist) as parents_ids FROM t WHERE id=6;
-- outputs:
-- parents_ids
-- -----------
-- 3
-- 1

Note that the last query does not output the "current" id (6).