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Flattening a Parent Child Hierarchy Expand / Collapse
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Posted Tuesday, March 01, 2011 2:00 AM
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Hi,

We are starting work on a BI project that is given data in a traditional Parent-Child Hierarchy format.

The Problem is that we need to Flatten the Hierarchy out the method that we have is to create a delimited string via a standard recursive CTE, then using a UDF string spliter, with a sample record set of just 9 rows, and 4 levels, the query curently takes around 1.5 seconds.

The actual record set we have to flatten is around 3-5K rows, and to complicate matters we need to run this as a low-latency, every 15 minutes, so its critical that we parse these structures as quickly as possible.

I have managed to pivot the dataset and get the leaf nodes correct, by using this script

WITH DirectReports(Name,Title, Manager, EmployeeID, ManagerId, EmployeeLevel,Sort)
AS
(SELECT CONVERT(varchar(255), e.FirstName + ' ' + e.LastName),
e.Title,
Convert(varchar, NULL) Manager,
e.EmployeeID,
convert(int,Null) ManagerId,
0,
CONVERT(varchar(255), '\'+e.FirstName + ' ' + e.LastName)

FROM dbo.MyEmployees AS e
WHERE e.ManagerID IS NULL
UNION ALL
SELECT
CONVERT(varchar(255), e.FirstName + ' ' + e.LastName),
e.Title,
Convert(varchar,d.Name) name,
e.EmployeeID,
convert(int,d.EmployeeID) as ManagerId,
EmployeeLevel + 1,
CONVERT (varchar(255), RTRIM(Sort) + '\' + FirstName + ' ' + LastName)

FROM dbo.MyEmployees AS e
JOIN DirectReports AS d ON e.ManagerID = d.EmployeeID
),

Piv AS (
Select *
FROM (Select d.EmployeeId,d.ManagerId,d.Name, d.EmployeeLevel,d.EmployeeLevel c,Sort
from DirectReports d
) T
PIVOT (MAX(Name) For EmployeeLevel IN ([0],[1],[2],[3],[4],[5],[6],[7],[8],[9])) p
)

Select EmployeeId,[0],[1],[2],[3],[4]
from Piv
order by Sort

The speed is about what we need at 1ms, however it returns this data set

Id 0 1 2 3 4
1 Ken Sánchez NULL NULL NULL NULL
273 NULL Brian Welcker NULL NULL NULL
16 NULL NULL David Bradley NULL NULL
23 NULL NULL NULL Mary Gibson NULL
274 NULL NULL Stephen Jiang NULL NULL
276 NULL NULL NULL Linda Mitchell NULL
275 NULL NULL NULL Michael Blythe NULL
285 NULL NULL Syed Abbas NULL NULL
286 NULL NULL NULL Lynn Tsoflias NULL

as you can see the nodes are Parent Levels are blank.

This is result set I'm that trying to get out.

Id Level0 Level1 Level2 Level3 Level4
1 Ken Sánchez NULL NULL NULL NULL
16 Ken Sánchez Brian Welcker David Bradley NULL NULL
23 Ken Sánchez Brian Welcker David Bradley Mary Gibson NULL
273 Ken Sánchez Brian Welcker NULL NULL NULL
274 Ken Sánchez Brian Welcker Stephen Jiang NULL NULL
275 Ken Sánchez Brian Welcker Stephen Jiang Michael Blythe NULL
276 Ken Sánchez Brian Welcker Stephen Jiang Linda Mitchell NULL
285 Ken Sánchez Brian Welcker Syed Abbas NULL NULL
286 Ken Sánchez Brian Welcker Syed Abbas Lynn Tsoflias NULL

Any pointers or advice gratefully accepted, I suspect theres a Self join back into the CTE or Source table But I cant for the life of me figure it out.


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Post #1071035
Posted Tuesday, March 01, 2011 3:09 AM


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The obvious issue with this sort of query is that you have to have a finite limit to the depth of recursion that can be displayed.

You may be better of , making this a display issue and doing the work in the presentation layer.

In any case , here's how you can handle this in SQL
Create table PrtChild
(
Id integer not null,
PrtId integer null,
Name varchar(20)
)
go
insert into PrtChild values(1,null,'Dave')
insert into PrtChild values(2,1,'Tom')
insert into PrtChild values(3,1,'Dick')
insert into PrtChild values(4,2,'Harry')
go

with cteTree
as
(

Select Id,PrtId,
Name as Path1,
cast(Null as varchar(255)) as Path2,
cast(Null as varchar(255)) as Path3,
cast(Null as varchar(255)) as Path4,
cast(Null as varchar(255)) as Path5,
0 as Level
from PrtChild
where PrtId is null
union all
Select Child.Id,
Child.PrtID,
Path1,
case when Level+1 = 1 then Name else Path2 end,
case when Level+1 = 2 then Name else Path3 end,
case when Level+1 = 3 then Name else Path4 end,
case when Level+1 = 4 then Name else Path5 end,
Level+1
from CteTree
join PrtChild child
on child.PrtId = CteTree.Id
)

select * from cteTree





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Post #1071067
Posted Tuesday, March 01, 2011 3:29 AM
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Thanks Dave, much appreciated.

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Post #1071076
Posted Friday, March 04, 2011 2:01 AM
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I managed to figure out a more dynamic way of doing this using a couple of recursive CTE's one to traverse downt he hierarchy the second to traverse up the heirarchy.

Heres the SQL code.

SET STATISTICS TIME ON;

WITH DirectReports(Name,Manager, EmployeeID, ManagerId, EmployeeLevel)
AS
(SELECT CONVERT(varchar(255), e.FirstName + ' ' + e.LastName),
Convert(varchar, NULL) Manager,
e.EmployeeID,
convert(int,Null) ManagerId,
0
FROM dbo.MyEmployees AS e
WHERE e.ManagerID IS NULL
UNION ALL
SELECT
CONVERT(varchar(255), e.FirstName + ' ' + e.LastName),
Convert(varchar,d.Name) name,
e.EmployeeID,
convert(int,d.EmployeeID) as ManagerId,
EmployeeLevel + 1
FROM dbo.MyEmployees AS e
JOIN DirectReports AS d ON e.ManagerID = d.EmployeeID

), X AS
(
Select Row_Number() OVER (ORDER BY EmployeeId) id,EmployeeID, Name, ManagerId, EmployeeLevel
From DirectReports
UNION ALL
SELECT
id,
x.EmployeeId,
CONVERT(varchar(255), e.FirstName + ' ' + e.LastName),
e.ManagerId,
EmployeeLevel-1
From X
JOIN dbo.MyEmployees as e on e.EmployeeId=x.ManagerId

)

Select id, EmployeeId,Max([0]),Max([1]),Max([2]),Max([3]),Max([4])
from (Select *
FROM (Select id,d.EmployeeId,d.ManagerId,d.Name, d.EmployeeLevel,d.EmployeeLevel c --,Sort
from x d
) T
PIVOT (MAX(Name) For EmployeeLevel IN ([0],[1],[2],[3],[4],[5],[6],[7],[8],[9])) p) piv
group by id,EmployeeID

It takes 3ms to run on a 9 row table, on a local DB.

In theory it should work for any Parent Child Hierarchy as long as you know the number of levels.



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SSC Guide to Posting and Best Practices
Post #1073147
Posted Sunday, March 06, 2011 10:11 AM


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Your problem is that you picked the wrong tradition

The adjacency list model is what people who grow up with recursive procedural code and assembly language pointer chains use. Switch this over to a Nested Sets model and finding all the subordinates is fast, self-join for any depth.

You will get the level in the hierarchy with a little math and can use that in the front end to format the display in the usual [-|+] file folders styel.


Books in Celko Series for Morgan-Kaufmann Publishing
Analytics and OLAP in SQL
Data and Databases: Concepts in Practice
Data, Measurements and Standards in SQL
SQL for Smarties
SQL Programming Style
SQL Puzzles and Answers
Thinking in Sets
Trees and Hierarchies in SQL
Post #1073862
Posted Monday, March 07, 2011 2:08 AM
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Thanks Joe, I come from an App dev background, and even though I've been writing SQL code for 8 years old habits are hard to get rid off. :)

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Post #1073991
Posted Wednesday, July 11, 2012 10:48 PM


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Jason-299789 (3/1/2011)
Hi,

We are starting work on a BI project that is given data in a traditional Parent-Child Hierarchy format.

The Problem is that we need to Flatten the Hierarchy out the method that we have is to create a delimited string via a standard recursive CTE, then using a UDF string spliter, with a sample record set of just 9 rows, and 4 levels, the query curently takes around 1.5 seconds.

The actual record set we have to flatten is around 3-5K rows, and to complicate matters we need to run this as a low-latency, every 15 minutes, so its critical that we parse these structures as quickly as possible.

I have managed to pivot the dataset and get the leaf nodes correct, by using this script

WITH DirectReports(Name,Title, Manager, EmployeeID, ManagerId, EmployeeLevel,Sort)
AS
(SELECT CONVERT(varchar(255), e.FirstName + ' ' + e.LastName),
e.Title,
Convert(varchar, NULL) Manager,
e.EmployeeID,
convert(int,Null) ManagerId,
0,
CONVERT(varchar(255), '\'+e.FirstName + ' ' + e.LastName)

FROM dbo.MyEmployees AS e
WHERE e.ManagerID IS NULL
UNION ALL
SELECT
CONVERT(varchar(255), e.FirstName + ' ' + e.LastName),
e.Title,
Convert(varchar,d.Name) name,
e.EmployeeID,
convert(int,d.EmployeeID) as ManagerId,
EmployeeLevel + 1,
CONVERT (varchar(255), RTRIM(Sort) + '\' + FirstName + ' ' + LastName)

FROM dbo.MyEmployees AS e
JOIN DirectReports AS d ON e.ManagerID = d.EmployeeID
),

Piv AS (
Select *
FROM (Select d.EmployeeId,d.ManagerId,d.Name, d.EmployeeLevel,d.EmployeeLevel c,Sort
from DirectReports d
) T
PIVOT (MAX(Name) For EmployeeLevel IN ([0],[1],[2],[3],[4],[5],[6],[7],[8],[9])) p
)

Select EmployeeId,[0],[1],[2],[3],[4]
from Piv
order by Sort

The speed is about what we need at 1ms, however it returns this data set

Id 0 1 2 3 4
1 Ken Sánchez NULL NULL NULL NULL
273 NULL Brian Welcker NULL NULL NULL
16 NULL NULL David Bradley NULL NULL
23 NULL NULL NULL Mary Gibson NULL
274 NULL NULL Stephen Jiang NULL NULL
276 NULL NULL NULL Linda Mitchell NULL
275 NULL NULL NULL Michael Blythe NULL
285 NULL NULL Syed Abbas NULL NULL
286 NULL NULL NULL Lynn Tsoflias NULL

as you can see the nodes are Parent Levels are blank.

This is result set I'm that trying to get out.

Id Level0 Level1 Level2 Level3 Level4
1 Ken Sánchez NULL NULL NULL NULL
16 Ken Sánchez Brian Welcker David Bradley NULL NULL
23 Ken Sánchez Brian Welcker David Bradley Mary Gibson NULL
273 Ken Sánchez Brian Welcker NULL NULL NULL
274 Ken Sánchez Brian Welcker Stephen Jiang NULL NULL
275 Ken Sánchez Brian Welcker Stephen Jiang Michael Blythe NULL
276 Ken Sánchez Brian Welcker Stephen Jiang Linda Mitchell NULL
285 Ken Sánchez Brian Welcker Syed Abbas NULL NULL
286 Ken Sánchez Brian Welcker Syed Abbas Lynn Tsoflias NULL

Any pointers or advice gratefully accepted, I suspect theres a Self join back into the CTE or Source table But I cant for the life of me figure it out.


Hi Jason,

Yeah, I realize that this thread is well over a year old but I hope you're still around because I found it very interesting. What I'd really like to know is "why". That is, why did you need to present the hierarchical data in a flattened format like this?

And, no... I'm not getting ready to start a "fight" over whether it's right or wrong. I'm just really curious as to what the actual business requirement to do this is. If you get the chance, I sure would like to hear about it.


--Jeff Moden
"RBAR is pronounced "ree-bar" and is a "Modenism" for "Row-By-Agonizing-Row".

First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column."

"Change is inevitable. Change for the better is not." -- 04 August 2013
(play on words) "Just because you CAN do something in T-SQL, doesn't mean you SHOULDN'T." --22 Aug 2013

Helpful Links:
How to post code problems
How to post performance problems
Post #1328658
Posted Tuesday, July 17, 2012 3:34 PM
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Hi Jeff,

Sorry for the delay, works been quite hectic as we try and clear the decks as much as possible before the Olympic chaos hits london.

The reason was that we were building a Data Warehouse off of Oracle Financials, which would hold 3+ years of data, with an estimateld 20 million rows in the balances and around the same in the transactions for every 12 months.

As there was an OLAP solution (SSAS) over the top, and natural parent child hierarchies were discounted as there were 8 seperate segments for the data to be analysed by, as there is a performance issue with Parent-child hierarchies in SSAS as they are not included in any Aggregation designs that you create.

The client also mentioned that they wanted to be able to add data to non-leaf level members in each hierarchy, hence the requrement to have each level act as a Leaf Level, an example of such data is budget numbers that cant be broken down below a certain grain without causing massive data expansion issues.

I'll try and post the DDL tomorrow for the final SP that I created which generically creates any Hierachy based on a point of Origin and the relevant HierarchyId that is passed in.

I know there are some improvements that I can make but it works and returns the data in a timely manner so its not a priority at the moment.

I hope this explains things a bit better, feel free to ask me any more questions if something isnt clear.

Regards

Jason.


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Post #1331113
Posted Wednesday, July 18, 2012 1:17 AM
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Jeff as per my last message, this is the DDL for the SP and source Table FND_FLEX_VALUE_NORM_HIERARCHY as well as the Execution plans and IO/Timing Stats

Just a little explanation of some of the files

BuildHierarchy.Txt file is the main Stored Proc, you might notice a couple of strange things, the first being a superluous IF 1=0, this is needed to interface with SSIS and return a column list from the output as SSIS doesnt play nicely with Temp tables.

The FND_FLEX_VALUE_NORM_HIERARCHY.Txt is the source table in Oracle Financials, and the key fields here are FLEX_VALUE_SET_ID (Type of Hierarchy), PARENT_FLEX_VALUE (Parental Node), CHILD_FLEX_VALUE_LOW (Child Range Start), CHILD_FLEX_VALUE_HIGH (Child Range End).

I've also attached sample data, to show the structure in Sample Data.Txt.

Its not a full tree as some are upwards 8-9 levels.


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SSC Guide to Posting and Best Practices


  Post Attachments 
Sample Data.txt (41 views, 2.73 KB)
BuildHierarchy.Txt (55 views, 18.24 KB)
EXEC Plan.txt (15 views, 17.99 KB)
HR Builder IO Stats.txt (10 views, 2.81 KB)
HR Builder Timing Stats.Txt (7 views, 1.18 KB)
Post #1331259
Posted Wednesday, July 18, 2012 9:47 AM


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Thanks, Jason... I'll have a look at this tonight after work.

BTW... thanks for taking the time for the explainations and the code even after so long. Quick look over says that you're limted to 12 levels for now. I'm pretty sure we can automatically beat the tar out of that.

As a side bar, why is there a "range" of child elements? I don't get that yet.


--Jeff Moden
"RBAR is pronounced "ree-bar" and is a "Modenism" for "Row-By-Agonizing-Row".

First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column."

"Change is inevitable. Change for the better is not." -- 04 August 2013
(play on words) "Just because you CAN do something in T-SQL, doesn't mean you SHOULDN'T." --22 Aug 2013

Helpful Links:
How to post code problems
How to post performance problems
Post #1331582
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