1795. Rearrange Products Table.sql

/*
Question 1795. Rearrange Products Table
Link: https://leetcode.com/problems/rearrange-products-table/description/?envType=problem-list-v2&envId=database

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.
*/

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