accessing parent nodes in same level in T-SQL - sql

Question

Let's say I have a database schema like this:
RowId ParentId Name
------ ---------- ------
1 NULL Level1
2 NULL Level2
3 1 Leaf1
4 1 Leaf2
5 2 Leaf1
6 3 LeafX
Basically, the tree would look as such:
Level1
Leaf1
LeafX
Leaf2
Level2
Leaf1
I need to extract all ancestor LEVEL of LeafX in the most efficient and dynamic way.
So it will output: Leaf1, Leaf2, and Leaf1 (of Level2)
How do I do this in T-SQL? Thanks

Answer 1

This will give you the result you want.
;with C as
(
select T.rowid,
T.parentid,
T.name,
1 as Lvl
from YourTable as T
where T.parentid is null
union all
select T.rowid,
T.parentid,
T.name,
C.Lvl + 1
from YourTable as T
inner join C
on T.parentid = C.rowid
)
select *
from C
where C.Lvl = (
select C.lvl-1
from C
where C.name = 'LeafX'
)
Update
And this might be faster for you. You have to test on your data.
declare #Level int;
with C as
(
select T.rowid,
T.parentid
from #t as T
where T.name = 'LeafX'
union all
select T.rowid,
T.parentid
from #t as T
inner join C
on T.rowid = C.parentid
)
select #Level = count(*) - 1
from C;
with C as
(
select T.rowid,
T.parentid,
T.name,
1 as Lvl
from #t as T
where T.parentid is null
union all
select T.rowid,
T.parentid,
T.name,
C.Lvl + 1
from #t as T
inner join C
on T.parentid = C.rowid
where C.Lvl < #Level
)
select *
from C
where C.Lvl = #Level;

Answer 2

There's a few methods to do that. My favourite is to create special table Trees_Parents, where you will store every parent for evere node.
So if have structure like that
RowId ParentId Name
------ ---------- ------
1 NULL Level1
2 NULL Level2
3 1 Leaf1
4 1 Leaf2
5 2 Leaf1
6 3 LeafX
your Trees_Parents table will looks like
RowId ParentId
------ ----------
1 1
2 2
3 3
3 1
4 4
4 1
5 5
5 2
6 6
6 1
6 3
then when you need to retrieve all children you just write
select RowID from Trees_Parents where ParentId = 1
I'm storing row self in this table to avoid unions, if you don't need it you can write
select RowID from Trees_Parents where ParentId = 1 and ParentId <> RowId
And for all parents you'll write
select ParentId from Trees_Parents where RowId = 6 and ParentId <> RowId
You can also store Table_Name in table Trees_Parents so you can use it for different tables
Another way is to write recursive WITH clause, but if your tree is big and it's not changing frequently I think it's better to store parents data in additional table

Answer 3

Well you can use recursive solution. You need to get all nodes with Depth = Depth of your node - 1
declare #Temp table (RowId int, ParentId int, Name nvarchar(128))
insert into #Temp
select 1, null, 'Level1' union all
select 2, null, 'Level2' union all
select 3, 1, 'Leaf1' union all
select 4, 1, 'Leaf2' union all
select 5, 2, 'Leaf3' union all
select 6, 3, 'LeafX';
with Parents
as
(
select T.RowId, 0 as Depth from #Temp as T where T.ParentId is null
union all
select T.RowId, P.Depth + 1
from Parents as P
inner join #Temp as T on T.ParentId = P.RowId
)
select T.Name
from Parents as P
outer apply (select TT.Depth from Parents as TT where TT.RowId = 6) as CALC
left outer join #Temp as T on T.RowId = P.RowId
where P.Depth = CALC.Depth - 1

Answer 4

declare #t table(rowid int, parentid int, name varchar(10))
insert #t values(1,NULL,'Level1')
insert #t values(2,NULL,'Level2')
insert #t values(3,1,'Leaf1')
insert #t values(4,1,'Leaf2')
insert #t values(5,2,'Leaf1')
insert #t values(6,3,'LeafX')
;with a as
(
select rowid, parentid, 0 level from #t where name = 'leafx'
union all
select t.rowid, t.parentid, level + 1 from #t t
join a on a.parentid = t.rowid
), b as
(
select rowid, parentid,name, 0 level from #t where parentid is null
union all
select t.rowid, t.parentid,t.name, level + 1
from b join #t t on b.rowid = t.parentid
)
select rowid, parentid, name from b
where level = (select max(level)-1 from a)
rowid parentid name
5 2 Leaf1
3 1 Leaf1
4 1 Leaf2