PL/pgSQL: finding all groups person belongs to (also indirectly) - sql

Question

Simple intro:
I have a database with users and groups.
Every user might be a member of one or more groups.
Every group might have one or more parent groups.
Schema:
CREATE TABLE users(
username VARCHAR(64) NOT NULL PRIMARY KEY,
password VARCHAR(64) NOT NULL,
enabled BOOLEAN NOT NULL);
CREATE TABLE groups (
id bigserial NOT NULL PRIMARY KEY,
group_name VARCHAR(64) NOT NULL);
CREATE TABLE groups_inheritance (
group_id bigint NOT NULL,
parent_group_id bigint NOT NULL,
CONSTRAINT fk_group_inheritance_group FOREIGN KEY(group_id) REFERENCES groups(id),
CONSTRAINT fk_group_inheritance_group_2 FOREIGN KEY(parent_group_id) REFERENCES groups(id),
CONSTRAINT unique_uk_groups_inheritance UNIQUE(group_id, parent_group_id));
CREATE TABLE group_members (
id bigint PRIMARY KEY,
username VARCHAR(64) NOT NULL,
group_id bigint NOT NULL,
CONSTRAINT fk_group_members_username FOREIGN KEY(username) REFERENCES users(username),
CONSTRAINT fk_group_members_group FOREIGN KEY(group_id) REFERENCES groups(id));
I'm looking for a PL/pgSQL function which finds all groups (their names) particular user belongs to.
Example:
group name: People,
group parent: null
group name: Students,
group parent: People
group name: Football_players,
group parent: People
group name: Basketball_players,
group parent: People
user name: Maciej,
groups : Students, Football_players
f("Maciej") = {"Students", "People", "Football_players"}
He belongs to "People" just because he belongs to "Students" or "Football_players". He is not a direct member of "People" group.
Thanks in advance!

Answer 1

WITH RECURSIVE group_ancestry AS (
SELECT group_id, username
FROM group_members
UNION
SELECT groups_inheritance.parent_group_id, username
FROM group_ancestry
JOIN groups_inheritance ON groups_inheritance.group_id = group_ancestry.group_id
)
SELECT username, group_id
FROM group_ancestry

Answer 2

If you have just one level of inheritance (as in example), then you could use such query:
WITH group_ids AS
(
SELECT group_id
FROM group_members
WHERE username LIKE 'Maciej'
)
SELECT group_name
FROM
(SELECT group_id FROM group_ids
UNION
SELECT DISTINCT parent_group_id
FROM groups_inheritance INNER JOIN group_ids USING(group_id)) g
INNER JOIN groups ON id = group_id;
Result:
group_name
------------------
People
Students
Football_players
(3 rows)
PL/pgSQL function:
DROP FUNCTION IF EXISTS f(varchar(64));
CREATE FUNCTION f(username varchar(64))
RETURNS text[] AS $$
DECLARE
gId bigint;
pgId bigint;
gName text;
result text[] = '{}';
BEGIN
FOR gId IN SELECT group_id FROM group_members WHERE username LIKE username
LOOP
SELECT INTO gName group_name FROM groupS WHERE id = gId;
result := result || gName;
FOR pgId IN SELECT parent_group_id FROM groups_inheritance WHERE group_id = gId
LOOP
SELECT INTO gName group_name FROM groups WHERE id = pgId;
IF NOT (result #> ARRAY[gName]) THEN
result := result || gName;
END IF;
END LOOP;
END LOOP;
RETURN result;
END $$
LANGUAGE 'plpgsql';
Result:
SELECT f('Maciej');
f
------------------------------------
{Students,People,Football_players}
(1 row)
However for nested parent groups I think that recursion should be suitable.
EDIT:
Here is recursion-based variant for nested parent groups:
CREATE OR REPLACE FUNCTION f_recursive(gIdParam bigint, resultArrayParam bigint[])
RETURNS bigint[] AS $$
DECLARE
pgId bigint;
resultArray bigint[];
BEGIN
FOR pgId IN SELECT parent_group_id FROM groups_inheritance WHERE group_id = gIdParam
LOOP
IF NOT (resultArrayParam #> ARRAY[pgId]) THEN
resultArray := resultArray || pgId;
resultArray := resultArray || f_recursive(pgId, resultArray);
END IF;
END LOOP;
RETURN resultArray;
END $$
LANGUAGE 'plpgsql';
CREATE OR REPLACE FUNCTION f(usernameParam varchar(64))
RETURNS text[] AS $$
DECLARE
gId bigint;
resultArray bigint[];
BEGIN
FOR gId IN SELECT group_id FROM group_members WHERE username LIKE usernameParam
LOOP
resultArray := resultArray || gId;
resultArray := resultArray || f_recursive(gId, resultArray);
END LOOP;
RETURN array_agg(group_name)
FROM groups INNER JOIN (SELECT unnest(resultArray)) u ON unnest = id;
END $$
LANGUAGE 'plpgsql';
Example insert:
INSERT INTO groups (id, group_name) VALUES
(1, 'People'), (2, 'Workers'), (3, 'Programmers'),
(4, 'AI-Programmers'), (5, 'Administators'), (6, 'Managers');
INSERT INTO groups_inheritance (group_id, parent_group_id) VALUES
(2, 1), (3, 2), (4, 3), (5, 2), (6, 2);
INSERT INTO users (username, password, enabled) VALUES
('Maciej', '12345', true);
INSERT INTO group_members (id, username, group_id) VALUES
(1, 'Maciej', 4), (2, 'Maciej', 5);
Result:
SELECT f('Maciej');
f
-----------------------------------------------------------
{AI-Programmers,Programmers,Workers,People,Administators}
(1 row)
Another way is to use WITH query along with RECURSIVE modifier as #araqnid shown.