CREATE TABLE category (
id int(10) unsigned NOT NULL AUTO_INCREMENT,
title varchar(255) NOT NULL,
parent_id int(10) unsigned DEFAULT NULL,
PRIMARY KEY (id),
FOREIGN KEY (parent_id) REFERENCES category (id)
ON DELETE CASCADE ON UPDATE CASCADE
);
CREATE TABLE `items` (
`id` int unsigned NOT NULL AUTO_INCREMENT,
`cat_id` int unsigned DEFAULT NULL,
`parent_id` int unsigned DEFAULT NULL,
`name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
PRIMARY KEY (`id`),
KEY `cat_id` (`cat_id`),
KEY `sub_id` (`parent_id`),
CONSTRAINT `cat_id` FOREIGN KEY (`cat_id`) REFERENCES `category` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `sub_id` FOREIGN KEY (`parent_id`) REFERENCES `category` (`parent_id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
BEGIN;
INSERT INTO `category` VALUES (1, 'Colazione', NULL);
INSERT INTO `category` VALUES (2, 'Pranzo', NULL);
INSERT INTO `category` VALUES (3, 'Primi piatti', 2);
INSERT INTO `category` VALUES (4, 'Second dish', 2);
INSERT INTO `category` VALUES (5, 'Other things for lunch', 2);
COMMIT;
-- ----------------------------
-- Records of items
-- ----------------------------
BEGIN;
INSERT INTO `items` VALUES (1, 1, NULL, 'Cornetto');
INSERT INTO `items` VALUES (2, 3, 2, 'Pasta al sugo 1');
INSERT INTO `items` VALUES (3, 3, 2, 'Pasta al sugo 2');
INSERT INTO `items` VALUES (4, 3, 2, 'Pasta al sugo 3');
INSERT INTO `items` VALUES (5, 3, 2, 'Pasta al sugo 1 X');
INSERT INTO `items` VALUES (6, 3, 2, 'Pasta al sugo 2 X');
INSERT INTO `items` VALUES (7, 4, 2, 'Pasta al sugo 3 X');
COMMIT;
with combine_trees as (
with make_tree as (
WITH RECURSIVE category_path AS
(
SELECT id, title, parent_id
FROM category
WHERE parent_id IS NULL
UNION ALL
SELECT c.id, c.title, c.parent_id
FROM category_path AS cp JOIN category AS c
ON cp.id = c.parent_id
)
SELECT cp.title, cp.id,
if(cp.id = category.id,
json_arrayagg(json_object('item_name', it.name)),
json_object(cp.title, json_object('items',json_arrayagg(json_array(json_object('item_name', it.name))))))
as tree
FROM category_path cp
join category on category.id = ifnull(cp.parent_id, cp.id)
Telegram: DB developers channel