Materializing the path of Nested Set hierarchy in T-SQL - sql

Question

I have a table containing details on my company's chart of accounts - this data is essentially stored in nested sets (on SQL Server 2014), with each record having a left and right anchor - there are no Parent IDs.
Sample Data:
ID LeftAnchor RightAnchor Name
1 0 25 Root
2 1 16 Group 1
3 2 9 Group 1.1
4 3 4 Account 1
5 5 6 Account 2
6 7 8 Account 3
7 10 15 Group 1.2
8 11 12 Account 4
9 13 14 Account 5
10 17 24 Group 2
11 18 23 Group 2.1
12 19 20 Account 1
13 21 22 Account 1
I need to materialize the path for each record, so that my output looks like this:
ID LeftAnchor RightAnchor Name MaterializedPath
1 0 25 Root Root
2 1 16 Group 1 Root > Group 1
3 2 9 Group 1.1 Root > Group 1 > Group 1.1
4 3 4 Account 1 Root > Group 1 > Group 1.1 > Account 1
5 5 6 Account 2 Root > Group 1 > Group 1.1 > Account 2
6 7 8 Account 3 Root > Group 1 > Group 1.1 > Account 3
7 10 15 Group 1.2 Root > Group 1 > Group 1.2
8 11 12 Account 4 Root > Group 1 > Group 1.2 > Acount 4
9 13 14 Account 5 Root > Group 1 > Group 1.2 > Account 5
10 17 24 Group 2 Root > Group 2
11 18 23 Group 2.1 Root > Group 2 > Group 2.1
12 19 20 Account 1 Root > Group 2 > Group 2.1 > Account 10
13 21 22 Account 1 Root > Group 2 > Group 2.1 > Account 11
Whilst I've managed to achieve this using CTEs, the query is deathly slow. It takes just shy of two minutes to run with around 1200 records in the output.
Here's a simplified version of my code:
;with accounts as
(
-- Chart of Accounts
select AccountId, LeftAnchor, RightAnchor, Name
from ChartOfAccounts
-- dirty great where clause snipped
)
, parents as
(
-- Work out the Parent Nodes
select c.AccountId, p.AccountId [ParentId]
from accounts c
left join accounts p on (p.LeftAnchor = (
select max(i.LeftAnchor)
from accounts i
where i.LeftAnchor<c.LeftAnchor
and i.RightAnchor>c.RightAnchor
))
)
, path as
(
-- Calculate the Account path for each node
-- Root Node
select c.AccountId, c.LeftAnchor, c.RightAnchor, 0 [Level], convert(varchar(max), c.name) [MaterializedPath]
from accounts c
where c.LeftAnchor = (select min(LeftAnchor) from chart)
union all
-- Children
select n.AccountId, n.LeftAnchor, n.RightAnchor, p.level+1, p.path + ' > ' + n.name
from accounts n
inner join parents x on (n.AccountId=x.AccountId)
inner join path p on (x.ParentId=p.AccountId)
)
select * from path order by LeftAnchor
Ideally this query should only take a couple of seconds (max) to run. I can't make any changes to the database itself (read-only connection), so can anyone come up with a better way to write this query?

Answer 1

After your comments, I realized no need for the CTE... you already have the range keys.
Example
Select A.*
,Path = Replace(Path,'>','>')
From YourTable A
Cross Apply (
Select Path = Stuff((Select ' > ' +Name
From (
Select LeftAnchor,Name
From YourTable
Where A.LeftAnchor between LeftAnchor and RightAnchor
) B1
Order By LeftAnchor
For XML Path (''))
,1,6,'')
) B
Order By LeftAnchor
Returns

Answer 2

First you can try to rearrange your preparing CTEs (accounts and parents) to have it that each CTE contains all data from previous, so you only use the last one in path CTE - no need for multiple joins:
;with accounts as
(
-- Chart of Accounts
select AccountId, LeftAnchor, RightAnchor, Name
from ChartOfAccounts
-- dirty great where clause snipped
)
, parents as
(
-- Work out the Parent Nodes
select c.*, p.AccountId [ParentId]
from accounts c
left join accounts p on (p.LeftAnchor = (
select max(i.LeftAnchor)
from accounts i
where i.LeftAnchor<c.LeftAnchor
and i.RightAnchor>c.RightAnchor
))
)
, path as
(
-- Calculate the Account path for each node
-- Root Node
select c.AccountId, c.LeftAnchor, c.RightAnchor, 0 [Level], convert(varchar(max), c.name) [MaterializedPath]
from parents c
where c.ParentID IS NULL
union all
-- Children
select n.AccountId, n.LeftAnchor, n.RightAnchor, p.level+1, p.[MaterializedPath] + ' > ' + n.name
from parents n
inner join path p on (n.ParentId=p.AccountId)
)
select * from path order by LeftAnchor
This should give some improvement (50% in my test), but to have it really better, you can split first half of preparing data into #temp table, put clustered index on ParentID column in #temp table and use it in second part
if (Object_ID('tempdb..#tmp') IS NOT NULL) DROP TABLE #tmp;
with accounts as
(
-- Chart of Accounts
select AccountId, LeftAnchor, RightAnchor, Name
from ChartOfAccounts
-- dirty great where clause snipped
)
, parents as
(
-- Work out the Parent Nodes
select c.*, p.AccountId [ParentId]
from accounts c
left join accounts p on (p.LeftAnchor = (
select max(i.LeftAnchor)
from accounts i
where i.LeftAnchor<c.LeftAnchor
and i.RightAnchor>c.RightAnchor
))
)
select * into #tmp
from parents;
CREATE CLUSTERED INDEX IX_tmp1 ON #tmp (ParentID);
With path as
(
-- Calculate the Account path for each node
-- Root Node
select c.AccountId, c.LeftAnchor, c.RightAnchor, 0 [Level], convert(varchar(max), c.name) [MaterializedPath]
from #tmp c
where c.ParentID IS NULL
union all
-- Children
select n.AccountId, n.LeftAnchor, n.RightAnchor, p.level+1, p.[MaterializedPath] + ' > ' + n.name
from #tmp n
inner join path p on (n.ParentId=p.AccountId)
)
select * from path order by LeftAnchor
Hard to tell on small sample data, but it should be an improvement. Please tell if you try it.

Answer 3

Seems odd to me that you don't have a Parent ID, but with the aid of an initial OUTER APPLY, we can generate a Parent ID and then run a standard recursive CTE.
Example
Declare #Top int = null --<< Sets top of Hier Try 12 (Just for Fun)
;with cte0 as (
Select A.*
,B.*
From YourTable A
Outer Apply (
Select Top 1 Pt=ID
From YourTable
Where A.LeftAnchor between LeftAnchor and RightAnchor and LeftAnchor<A.LeftAnchor
Order By LeftAnchor Desc
) B
)
,cteP as (
Select ID
,Pt
,LeftAnchor
,RightAnchor
,Lvl=1
,Name
,Path = cast(Name as varchar(max))
From cte0
Where IsNull(#Top,-1) = case when #Top is null then isnull(Pt ,-1) else ID end
Union All
Select r.ID
,r.Pt
,r.LeftAnchor
,r.RightAnchor
,p.Lvl+1
,r.Name
,cast(p.path + ' > '+r.Name as varchar(max))
From cte0 r
Join cteP p on r.Pt = p.ID
)
Select *
From cteP
Order By LeftAnchor
Returns