Select tree path in MySQL table - mysql

Question

I have a MySQL table like this:
| CategoryId | Name | CategoryParentId |
|------------|---------------|------------------|
| 0 | Tech Support | (null) |
| 1 | Configuration | 0 |
| 2 | Questions | 1 |
| 3 | Sales | (null) |
| 4 | Questions | 3 |
| 5 | Other | (null) |
This is the output I desire when a query the ID 2 (for example):
Tech Support/Configuration/Questions
How do I do this without having to do multiple joins?
Fiddle
EDIT: Not sure if is the best way to do this, but I solved by creating a function:
DELIMITER $$
CREATE FUNCTION get_full_tree (CategoryId int) RETURNS VARCHAR(200)
BEGIN
SET #CategoryParentId = (SELECT CategoryParentId FROM category c WHERE c.CategoryId = CategoryId);
SET #Tree = (SELECT Name FROM category c WHERE c.CategoryId = CategoryId);
WHILE (#CategoryParentId IS NOT NULL) DO
SET #ParentName = (SELECT Name FROM category c WHERE c.CategoryId = #CategoryParentId);
SET #Tree = CONCAT(#ParentName, '/', #Tree);
SET #CategoryParentId = (SELECT CategoryParentId FROM category c WHERE c.CategoryId = #CategoryParentId);
END WHILE;
RETURN #Tree;
END $$
DELIMITER ;
I can now do this query:
SELECT CategoryId, get_full_tree(CategoryId) FROM category

Answer 1

You could create a new table, lets name it as hierarchy (could be a better name) where we would store all the ancestry of a category.
CREATE TABLE `hierarchy` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`parent` int(11) NOT NULL,
`child` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB;
For example in this case for Questions i.e. ID->2 we will have the below entries:
id parent child
====================
6 0 2
7 1 2
8 2 2
For the whole example the content of the table would be:
id parent child
===========================
1 0 0
2 3 3
3 5 5
4 0 1
5 1 1
6 0 2
7 1 2
8 2 2
9 3 4
10 4 4
Now whenever you want to retrieve the whole ancestry of node execute the below query:
select name from category where id in (select parent from hierarchy where child = 2 order by id ASC)
The above query will return all the ancestry names for the Questions (ID->2) i.e.
name
==================
Tech Support
Configuration
Questions
For completeness shake below is the content for category table
id Name
============================
0 Tech Support
1 Configuration
2 Questions
3 Sales
4 Questions
5 Other
N.B. This is just an idea i am sure you can definitely build more elegant solution on top of it.

Answer 2

If you are using MySQL 8 or above you can use Common Table Expressions for recursive queries. Query would be the following
WITH RECURSIVE CategoryPath (CategoryId, Name, path) AS
(
SELECT CategoryId, Name, Name as path
FROM category
WHERE CategoryParentId IS NULL
UNION ALL
SELECT c.CategoryId, c.Name, CONCAT(cp.path, ' / ', c.Name)
FROM CategoryPath AS cp JOIN category AS c
ON cp.CategoryId = c.CategoryParentId
)
SELECT * FROM CategoryPath ORDER BY path;