How to generate an SQL query?

Question

MySQL

Hello, there are 2 tables
1) product

2) prod_to_cat

How to form a query to get something like this? Given that the product_id is taken from the first table

Answer 1

SELECT 
    `product_id`
    GROUP_CONCAT(`category_id`) AS 'categories'
FROM `prod_to_cat`
GROUP BY product_id