Linking together different columns in a SQL table? - sql

Question

I'm not very experienced with advance SQL queries, I'm familiar with basic statements and basic joins, currently trying to figure out how to write a query that seems to be out of my depth and I haven't been able to find a solution from google so far and I'm hoping somebody might be able to point me in the right direction.
The table I'm working with has an ID column, and a 'parent id' column.
I'm looking for all descendants of ID '1' - rows with a parent ID of '1', rows with a parent ID equal to any row's ID with a parent ID of '1' etc. Currently I've been doing this manually but there are hundreds of descendants so far and I feel like there's a way to put this into one query.
Any help would be appreciated, if this is unclear I can also try to clarify.
EDIT - I got it working with the following query:
with cteMappings as (
select map_id, parent_map_id, map_name
from admin_map
where map_id = '1'
union all
select a.map_id, a.parent_map_id, a.map_name
from admin_map a
inner join cteMappings m
on a.parent_map_id = m.map_id
)
select map_id, parent_map_id, map_name
from cteMappings

Answer 1

Sounds like it can be achieved by Common Table Expression:
DECLARE #temp TABLE (id INT IDENTITY(1, 1), parent_id INT);
INSERT #temp
SELECT NULL
UNION ALL
SELECT 1
UNION ALL
SELECT 2
UNION ALL
SELECT NULL
SELECT * FROM #temp
; WITH HierarchyTemp (id, parent_id, depth) AS (
SELECT id, parent_id, 0
FROM #temp
WHERE id = 1
UNION ALL
SELECT t.id, t.parent_id, ht.depth + 1
FROM #temp t
INNER JOIN HierarchyTemp ht ON ht.id = t.parent_id
)
SELECT *
FROM HierarchyTemp
So the above example is creating a table variable with 4 rows:
id parent_id
1 NULL
2 1
3 2
4 NULL
Result of descendent of id '1' (also including itself, but can be excluded with an additional WHERE clause):
id parent_id depth
1 NULL 0
2 1 1
3 2 2