Inner joining on to temp table and insert to table in MySql - mysql

Question

I have a list of strings. Each of them have categories which are separated out by a '/'.
For example:
animals/domestic/dog
animals/domestic/cat
What I want to do with these categories is to insert into a MySql categories table.
The table has 4 columns:
id (int auto increment), category_name (nvarchar), parent_id (int), is_active (bit)
The logic around inserting these should be as follows:
The main categories (animals) should have a parent_id of 0.
The child categories will have the id of their parent as parent_id.
There cannot be two active categories with the same category name.
I have tried to implement the following logic:
Get a distinct list of strings.
From these, get a distinct list of main categories.
Insert the distinct main categories to the categories table with a parent ID of 0.
Organise each of the categories in pairs and get distinct pairs:
(animals, domestic)
(domestic, dog)
(domestic, cat)
Get the matching id for each of the parent categories and insert in to the child's parent_id
SQL:
/*INSERT ALL THE FIRST PARENT CATEGORIES WITH A PARENT ID OF 0*/
INSERT INTO categories (category_name, parent_id, is_active)
VALUES ('animals', 0, 1);
/*INSERT ALL THE CATEGORIES IN PAIRS TO TEMP TABLE*/
CREATE TEMPORARY TABLE tempcat(parent nvarchar(256), child nvarchar(256));
INSERT INTO tempcat
VALUES ('animals', 'domestic'),('domestic', 'dog'),('domestic','cat');
/*INSERT INTO THE CATEGORIES TABLE*/
INSERT INTO categories(category_name, parent_id, is_active)
SELECT tempcat.child, categories.id, 1
FROM categories
INNER JOIN tempcat
ON categories.category_name = tempcat.parent;
WHERE categories.is_active = 1;
/*DISPOSE THE TEMPORARY TABLE*/
DROP TEMPORARY TABLE tempcat;
Issue:
After the query is run I expect 4 entries in the categories table.
But I only get 2.
I can see that the temp table has correct entries before doing the last inner join.
I can't seem to figure out why the categories table wouldn't have the other two rows.
Any guidance in the right direction is highly appreciated.
Update #1
Suppose the specifications said 'There cannot be two active categories with the same category name that had the same parent IDs'.
For example, if there were two strings as (animals/domestic/cat), (animals/outdoor/cat) there should be two entries for cat with IDs of domestic and outdoor as parent_id's.

Answer 1

CREATE TABLE categories (id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
category_name VARCHAR(64),
parent_id INT UNSIGNED NOT NULL DEFAULT 0,
is_active CHAR(1) NULL,
UNIQUE INDEX idx_name_active (category_name));
CREATE TABLE source_data (path TEXT);
INSERT INTO source_data VALUES ('animals/domestic/dog'), ('animals/domestic/cat');
CREATE PROCEDURE update_categories_table()
BEGIN
DECLARE cnt INT DEFAULT 0;
INSERT IGNORE INTO categories (category_name, parent_id, is_active)
SELECT SUBSTRING_INDEX(path, '/', 1), 0, '1'
FROM source_data;
iteration: LOOP
SELECT COUNT(*) INTO cnt
FROM source_data
WHERE LOCATE('/', path);
IF NOT cnt THEN
LEAVE iteration;
END IF;
INSERT IGNORE INTO categories (category_name, parent_id, is_active)
SELECT SUBSTRING_INDEX(SUBSTRING_INDEX(source_data.path, '/', 2), '/', -1),
categories.id,
'1'
FROM source_data, categories
WHERE SUBSTRING_INDEX(source_data.path, '/', 1) = categories.category_name;
UPDATE source_data
SET path = SUBSTRING(path FROM 1 + LOCATE('/', path));
END LOOP iteration;
TRUNCATE source_data;
END
call update_categories_table;
SELECT * FROM categories;
id | category_name | parent_id | is_active
-: | :------------ | --------: | :--------
1 | animals | 0 | 1
4 | domestic | 1 | 1
7 | dog | 4 | 1
8 | cat | 4 | 1
db<>fiddle here

Answer 2

In MySQL 8, you can do this with a single query:
with splits as (
select 1 as n, substring_index(cats, '/', 1) as cat, cats
from strings union all
select 2 as n, substring_index(substring_index(cats, '/', 2), '/', -1) as cat, cats
from strings
where cats like '%/%' union all
select 3 as n, substring_index(substring_index(cats, '/', 3), '/', -1) as cat, cats
from strings
where cats like '%/%/%'
),
splits_n as (
select s.*, dense_rank() over (order by n, cat) as new_id
from splits s
),
splits_np as (
select s.*, sp.new_id as parent_id
from splits_n s left join
splits_n sp
on sp.cats = s.cats and sp.n = s.n - 1
)
select distinct new_id as id, cat, parent_id, 1 as is_active
from splits_np s;
Here is a db<>fiddle.
Unfortunately, this is much more painful in earlier versions.