How can I use IF and CONCAT within SELECT - mysql

Question

I have this Adjacency List Model table
Table:
CREATE TABLE node_structure_data (
id INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
title VARCHAR(455) NOT NULL,
parent_id INT(10) UNSIGNED DEFAULT NULL,
PRIMARY KEY (id),
FOREIGN KEY (parent_id) REFERENCES node_structure_data (id)
ON DELETE CASCADE ON UPDATE CASCADE
);
Output:
id title parent_id
1 Division NULL
2 Site 1 1
3 Paper 2
4 ms1 3
5 Site 2 1
6 Paper 5
7 ms2 6
8 Site 3 1
9 Paper 8
10 ms3 9
So I have the following query that duplicates a Site 1 e.g. and its children.
In this case, the children are Paper with parent_id = 2 and ms1 with parent_id = 3
INSERT INTO node_structure_data (title,parent_id)
WITH recursive max_id AS (
SELECT MAX(id) AS id FROM node_structure_data
),
child_nodes AS (
SELECT
n.id,
title,
parent_id,
m.id+1 AS new_id,
parent_id AS new_parent_id
FROM
node_structure_data n
CROSS JOIN
max_id AS m
WHERE
title='Site 1'
UNION ALL
SELECT
n.id,
n.parent_id,
n.title,
#row_num:=IF(#row_num=0,c.new_id,0) + 1 + #row_num AS new_id,
c.new_id
FROM
child_nodes c
INNER JOIN
node_structure_data n ON n.parent_id = c.id
CROSS JOIN (
SELECT #row_num:=0 AS rn
) AS vars
)
SELECT title,new_parent_id FROM child_nodes ORDER BY new_id;
Output:
id title parent_id
1 Division NULL
2 Site 1 1
3 Paper 2
4 ms1 3
5 Site 2 1
6 Paper 5
7 ms2 6
8 Site 3 1
9 Paper 8
10 ms3 9
11 Site 1 1
12 Paper 11
13 ms1 12
As you can see Site 1 and its children got duplicated with a new unique id.
However for the duplicated Site title I want to have a prefix text Copy of for the DUPLICATED Site 1 title
I only want that prefix for a Site/parent_id = 1
So that the duplicated nodes should look like this:
id title parent_id
1 Division NULL
2 Site 1 1
3 Paper 2
4 ms1 3
5 Site 2 1
6 Paper 5
7 ms2 6
8 Site 3 1
9 Paper 8
10 ms3 9
11 Copy of Site 1 1
12 Paper 11
13 ms1 12
I have tried to implement the IF and CONCAT in the query but for some reason, it doesn't work, I don't get any errors but the output stays the same.
IF(n.title LIKE '%Site%', CONCAT("Copy of ", n.title), n.title),
If the title contains the text Site then I want to contact the prefix and the site title otherwise no concat.
Any ideas?
Any help is appreciated!!!

Answer 1

This solution shows how to insert a copy of a subtree and re-identify the descendants.
INSERT INTO node_structure_data (id, title, parent_id)
WITH RECURSIVE subtree AS (
SELECT
id,
(SELECT MAX(id) FROM node_structure_data) AS last_id,
CONCAT('Copy of ', title) AS title,
parent_id
FROM node_structure_data
WHERE id = 2 -- i.e. title = 'Site 1'
UNION ALL
SELECT
n.id,
s.last_id,
n.title,
n.parent_id
FROM subtree s
JOIN node_structure_data n ON s.id = n.parent_id
), new_id AS (
SELECT
id,
last_id + ROW_NUMBER() OVER (ORDER BY id) AS new_id,
title,
parent_id
FROM subtree
)
SELECT
n.new_id AS id,
n.title,
COALESCE(p.new_id, n.parent_id) AS parent_id
FROM new_id n
LEFT JOIN new_id p ON n.parent_id = p.id
Note that starting MySQL 8 setting user variables within expressions is deprecated and will be removed in a future release.
The following fiddle shows the results of each CTE - db<>fiddle