CREATE TABLE category(
    category_id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(20) NOT NULL,
    parent INT DEFAULT NULL
);

INSERT INTO category VALUES
    (1, 'ELECTRONICS', NULL),
    (2, 'TELEVISIONS', 1),
    (3, 'TUBE', 2),
    (4, 'LCD', 2),
    (5, 'PLASMA', 2),
    (6, 'PORTABLE ELECTRONICS', 1),
    (7, 'MP3 PLAYERS', 6),
    (8, 'FLASH', 7),
    (9, 'CD PLAYERS', 6),
    (10, '2 WAY RADIOS', 6);

SELECT *
FROM category
ORDER BY category_id;