如何只获取第一层深度子节点？

Question

我正在使用树存储。 闭包 Table 模式。

https://towardsdatascience.com/closure-table-pattern-to-model-hierarchies-in-nosql-c1be6a87e05b

如何获取没有孙、曾孙的子节点？例如从祖先C得到子孙G、H、F

下面我以ClosureTable数据库为例

数据库关闭Table

-- phpMyAdmin SQL Dump
-- version 5.1.0
-- https://www.phpmyadmin.net/
--
-- Host: localhost
-- Generation Time: Aug 02, 2021 at 01:15 PM
-- Server version: 8.0.25
-- PHP Version: 8.0.3

SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
START TRANSACTION;
SET time_zone = "+00:00";


/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8mb4 */;

--
-- Database: `closure_table`
--

-- --------------------------------------------------------

--
-- Table structure for table `category_name`
--

CREATE TABLE `category_name` (
  `id` bigint NOT NULL,
  `name` varchar(255) COLLATE utf8mb4_ru_0900_ai_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_ru_0900_ai_ci;

--
-- Dumping data for table `category_name`
--

INSERT INTO `category_name` (`id`, `name`) VALUES
(1, 'Electronics'),
(2, 'Computers'),
(3, 'Accessories & Supplies'),
(4, 'Camera & Photo'),
(5, 'Computer accessories and peripherals'),
(6, 'Computer components'),
(7, 'Audio & Video Accessories'),
(8, 'Camera & Photo Accessories'),
(9, 'Accessories'),
(10, 'Bags & Cases'),
(11, 'Audio & Video Accessories'),
(12, 'Blank Media'),
(13, 'Computer screws'),
(14, 'Table Barebones'),
(15, '3D Glasses'),
(16, 'Antennas'),
(17, 'Accessory Bundles'),
(18, 'Bags & Cases'),
(19, 'Accessory Kits'),
(20, 'Bags & Cases'),
(21, 'Bag & Case Accessories'),
(22, 'Binocular Cases'),
(23, 'Computer headsets'),
(24, 'Computer microphones'),
(25, 'Discs BD-R'),
(26, 'Discs BD-RE'),
(27, 'bolts'),
(28, 'frame'),
(29, 'lamps'),
(30, 'coasters');

-- --------------------------------------------------------

--
-- Table structure for table `tree_path`
--

CREATE TABLE `tree_path` (
  `children` bigint NOT NULL,
  `parent` bigint NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_ru_0900_ai_ci;

--
-- Dumping data for table `tree_path`
--

INSERT INTO `tree_path` (`children`, `parent`) VALUES
(1, 1),
(3, 1),
(4, 1),
(7, 1),
(8, 1),
(9, 1),
(10, 1),
(15, 1),
(16, 1),
(17, 1),
(18, 1),
(19, 1),
(20, 1),
(21, 1),
(22, 1),
(2, 2),
(5, 2),
(6, 2),
(11, 2),
(12, 2),
(13, 2),
(14, 2),
(23, 2),
(24, 2),
(25, 2),
(26, 2),
(27, 2),
(28, 2),
(29, 2),
(30, 2),
(3, 3),
(7, 3),
(8, 3),
(15, 3),
(16, 3),
(17, 3),
(18, 3),
(4, 4),
(9, 4),
(10, 4),
(19, 4),
(20, 4),
(21, 4),
(22, 4),
(5, 5),
(11, 5),
(12, 5),
(23, 5),
(24, 5),
(25, 5),
(26, 5),
(6, 6),
(13, 6),
(14, 6),
(27, 6),
(28, 6),
(29, 6),
(30, 6),
(7, 7),
(15, 7),
(16, 7),
(8, 8),
(17, 8),
(18, 8),
(9, 9),
(19, 9),
(20, 9),
(10, 10),
(21, 10),
(22, 10),
(11, 11),
(23, 11),
(24, 11),
(12, 12),
(25, 12),
(26, 12),
(13, 13),
(27, 13),
(28, 13),
(14, 14),
(29, 14),
(30, 14),
(15, 15),
(16, 16),
(17, 17),
(18, 18),
(19, 19),
(20, 20),
(21, 21),
(22, 22),
(23, 23),
(24, 24),
(25, 25),
(26, 26),
(27, 27),
(28, 28),
(29, 29),
(30, 30);

--
-- Indexes for dumped tables
--

--
-- Indexes for table `category_name`
--
ALTER TABLE `category_name`
  ADD PRIMARY KEY (`id`);

--
-- Indexes for table `tree_path`
--
ALTER TABLE `tree_path`
  ADD PRIMARY KEY (`children`,`parent`),
  ADD KEY `FK_PARENT` (`parent`);

--
-- AUTO_INCREMENT for dumped tables
--

--
-- AUTO_INCREMENT for table `category_name`
--
ALTER TABLE `category_name`
  MODIFY `id` bigint NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=31;

--
-- Constraints for dumped tables
--

--
-- Constraints for table `tree_path`
--
ALTER TABLE `tree_path`
  ADD CONSTRAINT `FK_CHILDREN` FOREIGN KEY (`children`) REFERENCES `category_name` (`id`) ON DELETE CASCADE,
  ADD CONSTRAINT `FK_PARENT` FOREIGN KEY (`parent`) REFERENCES `category_name` (`id`) ON DELETE CASCADE;
COMMIT;

/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;

Answer 1

这是一个解决方案：

select p1.* from tree_path as p1
left outer join (tree_path as p2 join tree_path as p3 on p2.children = p3.parent)
 on p2.parent = p1.parent 
 and p3.children = p1.children 
 and p2.parent <> p2.children 
 and p3.parent <> p3.children
where p1.parent = 3 and p2.parent is NULL;
+----------+--------+
| children | parent |
+----------+--------+
|        3 |      3 |
|        7 |      3 |
|        8 |      3 |
+----------+--------+

更改 p1.parent=7 并得到以下输出：

+----------+--------+
| children | parent |
+----------+--------+
|        7 |      7 |
|       15 |      7 |
|       16 |      7 |
+----------+--------+

它是这样工作的：直系子节点是后代，其中存在从父节点到子节点的路径，但没有从父节点通过第三个节点到子节点的路径。所以我们尝试加入这样的路径（p2->p3），如果找到none，那么p2和p3的所有列都将为NULL。

如何只获取第一层深度子节点？

How to get only the first level of depth child nodes?

mysql

transitive-closure-table