View Hierarchical data as columns in sql - mysql

Question

I have a self referencing table to store a hierarchy.
vehicle_id
vehicle_name
parent_vehicle_id
1
social_media
NULL
2
facebook
1
3
instagram
1
4
stories
2
5
reel
3
6
igtv
3
using a cte, I am able to get the vehicle levels like so
with vehicle_tree (vehicle_id, vehicle_name, parent_vehicle_id, veh_level)
as
(
select v.vehicle_id, v.vehicle_name, v.parent_vehicle_id, 1 as veh_level from vehicle as v where v.parent_vehicle_id is null
union all
select sub_veh.vehicle_id, sub_veh.vehicle_name, sub_veh.parent_vehicle_id, vt.veh_level + 1 from vehicle as sub_veh
inner join vehicle_tree as vt
on vt.vehicle_id = sub_veh.parent_vehicle_id
where sub_veh.parent_vehicle_id is not null
)
select * from vehicle_tree
with the output
vehicle_id
vehicle_name
parent_vehicle_id
veh_level
1
social_media
NULL
1
2
facebook
1
2
3
instagram
1
2
5
reel
3
3
6
igtv
3
3
4
stories
2
3
What I would like to have, is to view the hierarchies as columns rather than rows something like this
1_id
1
2_id
2
3_id
3
1
social_media
2
facebook
4
stories
1
social_media
3
instagram
5
reel
1
social_media
3
instagram
6
igtv
I have gotten as far as this
with vehicle_tree (vehicle_id, vehicle_name, parent_vehicle_id, veh_level)
as
(
select v.vehicle_id, v.vehicle_name, v.parent_vehicle_id, 1 as veh_level from vehicle as v where v.parent_vehicle_id is null
union all
select sub_veh.vehicle_id, sub_veh.vehicle_name, sub_veh.parent_vehicle_id, vt.veh_level + 1 from vehicle as sub_veh
inner join vehicle_tree as vt
on vt.vehicle_id = sub_veh.parent_vehicle_id
where sub_veh.parent_vehicle_id is not null
)
select * from vehicle_tree l1
left outer join vehicle_tree l2 on l2.veh_level = 2 and l1.vehicle_id = l2.parent_vehicle_id
left outer join vehicle_tree l3 on l3.veh_level = 3 and l2.vehicle_id = l3.parent_vehicle_id
where l1.veh_level = 1
which gives the output that I expect but I would like to have some form of a recursive solution on the left outer joins instead
vehicle_id
vehicle_name
parent_vehicle_id
veh_level
vehicle_id
vehicle_name
parent_vehicle_id
veh_level
vehicle_id
vehicle_name
parent_vehicle_id
veh_level
1
social_media
NULL
1
2
facebook
1
2
4
stories
2
3
1
social_media
NULL
1
3
instagram
1
2
5
reel
3
3
1
social_media
NULL
1
3
instagram
1
2
6
igtv
3
3
Kindly advise how I can achieve the same output via a recursive function. I would prefer a solution that could be used on any engine but MS SQL will suffice for now

Answer 1

Because a SQL query returns a fixed set of columns, you can just use explicit JOINs to get the names in different columns:
select vt.*, vt2.*, vt3.*
from vehicle_tree vt left join
vehicle_tree vt2
on vt2.parent_vehicle_id = vt.vehicle_id left join
vehicle_tree vt3
on vt3.parent_vehicle_id = vt2.vehicle_id left join
where vt.parent_vehicle_id is null