mysql 无限级

-- 创建示例表
CREATE TABLE categories (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255),
    parent_id INT,
    FOREIGN KEY (parent_id) REFERENCES categories(id)
);

-- 插入示例数据
INSERT INTO categories (name, parent_id) VALUES
('Electronics', NULL),
('Computers', 1),
('Laptops', 2),
('Desktops', 2),
('Smartphones', 1),
('Cameras', 1);

-- 递归查询子节点
WITH RECURSIVE category_tree AS (
    SELECT id, name, parent_id, 1 as level
    FROM categories
    WHERE parent_id IS NULL
    UNION ALL
    SELECT c.id, c.name, c.parent_id, ct.level + 1
    FROM categories c
    JOIN category_tree ct ON c.parent_id = ct.id
)
SELECT * FROM category_tree;