Flatten the tree path in SQL server Hierarchy ID

Question

I am using SQL Hierarchy data type to model a taxonomy structure in my application. The taxonomy can have the same name in different levels

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During the setup this data needs to be uploaded via an excel sheet.

Before inserting any node I would like to check if the node at a particular path already exists so that I don't duplicate the entries. What is the easiest way to check if the node @ particular absolute path already exists or not?

for e.g Before inserting say "Retail" under "Bank 2" I should be able to check "/Bank 2/Retail" is not existing

Is there any way to provide a flattened representation of the entire tree structure so that I can check for the absolute path and then proceed?

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It seems from your example and tag that you already know the answer - store this in a `hierarchyid` and use `ToString` to convert each node to a string path then compare. You might need to insert into a staging table first — Nick.Mc, Sep 23 '14 at 08:38
The Path column I have is the ToString() representation. I need to be able to build the Flattened tree path. I currently don't know the way to get the Falttened Tree Path — Sharath Chandra, Sep 23 '14 at 09:10

JotaBe · Accepted Answer · 2014-09-23T09:11:20.523

Yes, you can do it using a recursive CTE.

In each iteration of the query you can append a new level of the hierarchy name.

There are lots of examples of this technique on the internet.

For example, with this sample data:

CREATE TABLE Test
(id INT,
parent_id INT null,
NAME VARCHAR(50)
)

INSERT INTO Test VALUES(1, NULL, 'L1')
INSERT INTO Test VALUES(2, 1, 'L1-A')
INSERT INTO Test VALUES(3, 2, 'L1-A-1')
INSERT INTO Test VALUES(4, 2, 'L1-A-2')
INSERT INTO Test VALUES(5, 1, 'L1-B')
INSERT INTO Test VALUES(6, 5, 'L1-B-1')
INSERT INTO Test VALUES(7, 5, 'L1-B-2')

you can write a recursive CTE like this:

WITH H AS
(
    -- Anchor: the first level of the hierarchy
    SELECT id, parent_id, name, CAST(name AS NVARCHAR(300)) AS path 
    FROM Test 
    WHERE parent_id IS NULL      
UNION ALL
    -- Recursive: join the original table to the anchor, and combine data from both  
    SELECT T.id, T.parent_id, T.name, CAST(H.path + '\' + T.name AS NVARCHAR(300)) 
    FROM Test T INNER JOIN H ON T.parent_id = H.id
)
-- You can query H as if it was a normal table or View
SELECT * FROM H
   WHERE PATH = 'L1\L1-A' -- for example to see if this exists

The result of the query (without the where filter) looks like this:

1  NULL  L1      L1
2  1     L1-A    L1\L1-A
5  1     L1-B    L1\L1-B
6  5     L1-B-1  L1\L1-B\L1-B-1
7  5     L1-B-2  L1\L1-B\L1-B-2
3  2     L1-A-1  L1\L1-A\L1-A-1
4  2     L1-A-2  L1\L1-A\L1-A-2

Flatten the tree path in SQL server Hierarchy ID

1 Answers1