SELECT unnest(array[1, 2, 3, 4, 5]) AS num;

 num
-----
   1
   2
   3
   4
   5
(5 rows)

CREATE TABLE categories (
    category_id SERIAL PRIMARY KEY,
    category_name VARCHAR(50)
);

INSERT INTO categories (category_name) VALUES ('Electronics'), ('Clothing'), ('Furniture');

CREATE TABLE products (
    product_id SERIAL PRIMARY KEY,
    product_name VARCHAR(50),
    product_price NUMERIC,
    product_categories INT[]
);

INSERT INTO products (product_name, product_price, product_categories) VALUES 
('Laptop', 1000, ARRAY[1]),
('T-Shirt', 20, ARRAY[2]),
('Couch', 500, ARRAY[3,2]),
('Headphones', 100, ARRAY[1,2]);

SELECT p.product_name, p.product_price, c.category_name
FROM products p
JOIN unnest(p.product_categories) AS category_id ON true
JOIN categories c ON c.category_id = category_id;

 product_name | product_price | category_name
--------------+---------------+---------------
 Laptop       | 1000          | Electronics
 T-Shirt      | 20            | Clothing
 Couch        | 500           | Furniture
 Couch        | 500           | Clothing
 Headphones   | 100           | Electronics
 Headphones   | 100           | Clothing
(6 rows)

SELECT unnest(array[[1, 2, 3], [4, 5, 6]]) AS num;

 num
-----
   1
   2
   3
   4
   5
   6
(6 rows)