Create and Maintain COMPLEX HIERARCHIES easily

CREATE AND MAITAIN MANY-MANY HIERARCHY (SQL CODE with DATASET provided)
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www.db-tools.com https://www.linkedin.com/in/sreenivasulu-kandakuru-72687a25
CREATE AND MAINTAIN COMPLEX HIERARCHYS
This article is dedicated to my GURU Bill Karwin. He had published a best article
in the whole web about building hierarchy. Yes building hierarchy which is a holy grail
for Data Architects / Data Modeler / Data Scientists / Data Analysts..

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Link published by Bill https://www.slideshare.net/billkarwin/models-for-hierarchical-data

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I will talk ONLY about the Closure Table Design which is the best design for updating
/deleting and as well as maintaining the hierarchy (highlighted below)

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SCOPE OF THE PRESENTATION ............................................................................................................................................................................................................ 5
Create Structures and populate initial data set............................................................................................................................................................................... 6
Let’s Try few SQL queries to generate the ‘depth of hierarchy’.................................................................................................................................................. 8
Add a node and its children ............................................................................................................................................................................................................. 9
Let’s Try few SQL queries to generate the ‘depth of hierarchy’ after addition......................................................................................................................... 11
‘Generated Hierarchy’ after addition looks like this ................................................................................................................................................................. 12
Delete a node and its children....................................................................................................................................................................................................... 13
After Delete It would look like this............................................................................................................................................................................................ 14
Let’s Try few SQL queries to generate the ‘depth of hierarchy’ after DELETION...................................................................................................................... 15
‘Generated Hierarchy Levels’ After delete................................................................................................................................................................................. 16
Update a node and its children...................................................................................................................................................................................................... 17
Our objective to achieve after update....................................................................................................................................................................................... 18
Let’s Try Updating the Hierarchy............................................................................................................................................................................................... 19
‘Generated Hierarchy Levels’ After update............................................................................................................................................................................... 20

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SCOPE OF THE PRESENTATION
I will cover adding a node , deleting a node , updating a node . An updated hierarchy is
generated after each operation which would clearly show how easily a hierarchy
can be maintained

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Create Structures and populate initial data set
CREATE TABLE dbo.product_hierarchy1
(
id INT NOT NULL,
parent_id INT NULL
)
INSERT INTO dbo.product_hierarchy1 (id, parent_id)
VALUES
(1, NULL),
(2, 1),
(3, 1),
(4, 2)

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The hierarchy diagram of the initial dataset looks like this below
ow

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Let’s Try few SQL queries to generate the ‘depth of hierarchy’
WITH product_hierarchy_cte AS
(
SELECT
id AS ancestor,
id AS descendant,
0 AS depth
FROM dbo.product_hierarchy1
UNION ALL
SELECT
CTE.ancestor AS ancestor,
C.id AS descendant,
CTE.depth + 1 AS depth
FROM dbo.product_hierarchy1 AS C
JOIN product_hierarchy_cte AS CTE
ON C.parent_id = CTE.descendant
)
SELECT * FROM product_hierarchy_cte

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Add a node and its children
select * into dbo.product_hierarchy3 from dbo.product_hierarchy1
INSERT INTO dbo.product_hierarchy3 (id, parent_id)
VALUES
(5, 3),
(6, 4),
(7, 4),
(8, 5),
(9, 5)

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The hierarchy diagram now looks like this below

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Let’s Try few SQL queries to generate the ‘depth of hierarchy’ after addition
WITH product_hierarchy_cte3 AS
(
SELECT
id AS ancestor,
id AS descendant,
0 AS depth
UNION ALL
SELECT
C.id AS descendant,
JOIN product_hierarchy_cte3 AS CTE
)
SELECT * FROM product_hierarchy_cte3

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‘Generated Hierarchy’ after addition looks like this

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Delete a node and its children
Let’s delete node 5
Before Delete DataSet

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After Delete It would look like this

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Let’s Try few SQL queries to generate the ‘depth of hierarchy’ after DELETION
delete from product_hierarchy3 where parent_id = 5
delete from product_hierarchy3 where id = 5
(
SELECT
id AS ancestor,
id AS descendant,
0 AS depth
UNION ALL
SELECT
C.id AS descendant,
)
SELECT * FROM product_hierarchy_cte3

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‘Generated Hierarchy Levels’ After delete

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Update a node and its children
Let’s Update 4 to 10 from the initial data set which was this

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Our objective to achieve after update

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Let’s Try Updating the Hierarchy
select * from dbo.[product_hierarchy3]
update [product_hierarchy3] set id = 10 where id = 4
update [product_hierarchy3] set parent_id = 10 where parent_id = 4
(
SELECT
id AS ancestor,
id AS descendant,
0 AS depth
UNION ALL
SELECT
C.id AS descendant,
)
select * from product_hierarchy_cte4

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‘Generated Hierarchy Levels’ After update

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Create and Maintain COMPLEX HIERARCHIES easily

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