Query for updating a node in a hierarchial tree structure

However once have in memory the tree data the application need a way to save them for future use.

SQL database can be a good solution but, in this case, we need a way to store data in efficient mode. IMPORTANT NOTE: Please note that I'm not the original author of this article.

Try picturing our electronics categories this way: Notice how our hierarchy is still maintained, as parent categories envelop their children.

query for updating a node in a hierarchial tree structure-4

For example, when showing the PORTABLE ELECTRONICS category, we will want to show MP3 PLAYERS, CD PLAYERS, and 2 WAY RADIOS, but not FLASH.

This can be easily accomplished by adding a HAVING clause to our previous query: SELECT node.name, (COUNT(parent.name) - (sub_tree.depth 1)) AS depth FROM nested_category AS node, nested_category AS parent, nested_category AS sub_parent, ( SELECT node.name, (COUNT(parent.name) - 1) AS depth FROM nested_category AS node, nested_category AS parent WHERE BETWEEN AND AND = 'PORTABLE ELECTRONICS' GROUP BY ORDER BY )AS sub_tree WHERE BETWEEN AND AND BETWEEN sub_AND sub_AND sub_= sub_GROUP BY HAVING depth CREATE TABLE product( product_id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR(40), category_id INT NOT NULL ); INSERT INTO product(name, category_id) VALUES('20" TV',3),('36" TV',3), ('Super-LCD 42"',4),('Ultra-Plasma 62"',5),('Value Plasma 38"',5), ('Power-MP3 5gb',7),('Super-Player 1gb',8),('Porta CD',9),('CD To go!

What I would like to focus on in this article is a different approach, commonly referred to as the Nested Set Model.

In the Nested Set Model, we can look at our hierarchy in a new way, not as nodes and lines, but as nested containers.

The deletion of a node is based off of the lft and rght values of the entity.


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