Multilevel Users in the Database table - mysql

Question

I am having one table users in which I have one field 'id' and another field is 'parent id'. Also I have expected target field in the users table.
I am having list of users till the 8th level hierarchy. Where A is parent of B and B is parent of C and so on.
e.g
A level 0
|
B level 1
|
c level 2
Now when I am looking for user A. I want to get the all the sub users using sql query 'expected target'.
i.e. When I use id = id of A then I can see the expected target of A,B,C etc.
If expected_targets for A, B and C are 1000, 500 , 200 respectively the output should be like :
id parent_id expected_target
A_id 1000
B_id A_id 500
C_id B_id 200

Answer 1

this will do the job - http://sqlfiddle.com/#!2/0de1f/7:
select u1.id, u1.parent_id, u1.expected_target
from users u1
left join users u2 on u1.parent_id = u2.id
left join users u3 on u2.parent_id = u3.id
left join users u4 on u3.parent_id = u4.id
left join users u5 on u4.parent_id = u5.id
left join users u6 on u5.parent_id = u6.id
left join users u7 on u6.parent_id = u7.id
left join users u8 on u7.parent_id = u8.id
where :A_id in (u1.id, u2.id, u3.id, u4.id, u5.id,
u6.id, u7.id, u8.id, u8.parent_id)

Answer 2

SET search_path='tmp';
DROP TABLE targets CASCADE;
CREATE TABLE targets
( id integer not null primary key
, parent_id integer references targets(id)
, expected_target integer
);
INSERT INTO targets(id,parent_id,expected_target) VALUES
(1,NULL, 1000), (2,1, 500), (3,2, 200);
WITH RECURSIVE zzz AS (
SELECT t0.id, t0.parent_id
, 0::integer AS level
, t0.expected_target
FROM targets t0
WHERE t0.parent_id IS NULL
UNION
SELECT t1.id, t1.parent_id
, 1+zzz.level AS level
, t1.expected_target
FROM targets t1
JOIN zzz ON zzz.id = t1.parent_id
)
SELECT * FROM zzz
;
OUTPUT:
SET
DROP TABLE
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "targets_pkey" for table "targets"
CREATE TABLE
INSERT 0 3
id | parent_id | level | expected_target
----+-----------+-------+-----------------
1 | | 0 | 1000
2 | 1 | 1 | 500
3 | 2 | 2 | 200
(3 rows)
UPDATE: if you don't want the whole tree, the true tree and nothing but the tree but only a subtree part of it, you can of course change the conditions a bit:
WITH RECURSIVE zzz AS (
SELECT t0.id, t0.parent_id
, 0::integer AS level
, t0.expected_target
FROM targets t0
-- WHERE t0.parent_id IS NULL
WHERE t0.id = 2
UNION
SELECT t1.id, t1.parent_id
, 1+zzz.level AS level
, t1.expected_target
FROM targets t1
JOIN zzz ON zzz.id = t1.parent_id
)
SELECT * FROM zzz
;

Answer 3

As this is tagged with PostgreSQL:
with recursive users_tree as (
select id,
parent_id,
expected_target,
1 as level
from users
where id = 'A_id'
union all
select c.id,
c.parent_id,
c.expected_target,
p.level + 1
from users c
join users_tree p on c.parent_id = p.id
)
select *
from users_tree
MySQL is not advanced enough to support this. There you'll need to do a self-join for each level.