Rearrange products table

#
# Table: Products
# +-------------+---------+
# | Column Name | Type    |
# +-------------+---------+
# | product_id  | int     |
# | store1      | int     |
# | store2      | int     |
# | store3      | int     |
# +-------------+---------+
# product_id is the primary key (column with unique values) for this table.
# Each row in this table indicates the product's price in 3 different stores: store1, store2, and store3.
# If the product is not available in a store, the price will be null in that store's column.
# Write a solution to rearrange the Products table so that each row has (product_id, store, price). If a product is not available in a store, do not include a row with that product_id and store combination in the result table.
# Return the result table in any order.
# The result format is in the following example.
# Example 1:
# Input:
# Products table:
# +------------+--------+--------+--------+
# | product_id | store1 | store2 | store3 |
# +------------+--------+--------+--------+
# | 0          | 95     | 100    | 105    |
# | 1          | 70     | null   | 80     |
# +------------+--------+--------+--------+
# Output:
# +------------+--------+-------+
# | product_id | store  | price |
# +------------+--------+-------+
# | 0          | store1 | 95    |
# | 0          | store2 | 100   |
# | 0          | store3 | 105   |
# | 1          | store1 | 70    |
# | 1          | store3 | 80    |
# +------------+--------+-------+
# Explanation:
# Product 0 is available in all three stores with prices 95, 100, and 105 respectively.
# Product 1 is available in store1 with price 70 and store3 with price 80. The product is not available in store2.
#

# Write your MySQL query statement below

SELECT product_id, 'store1' AS store, store1 AS price FROM Products WHERE store1 IS NOT NULL
UNION ALL
SELECT product_id, 'store2' AS store, store2 AS price FROM Products WHERE store2 IS NOT NULL
UNION ALL
SELECT product_id, 'store3' AS store, store3 AS price FROM Products WHERE store3 IS NOT NULL;