Description
https://leetcode.com/problems/rearrange-products-table/
Table: Products
+-------------+---------+ | Column Name | Type | +-------------+---------+ | product_id | int | | store1 | int | | store2 | int | | store3 | int | +-------------+---------+ product_id is the primary key 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 an SQL query 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 query result format is in the following example:
Products table: +------------+--------+--------+--------+ | product_id | store1 | store2 | store3 | +------------+--------+--------+--------+ | 0 | 95 | 100 | 105 | | 1 | 70 | null | 80 | +------------+--------+--------+--------+ Result table: +------------+--------+-------+ | product_id | store | price | +------------+--------+-------+ | 0 | store1 | 95 | | 0 | store2 | 100 | | 0 | store3 | 105 | | 1 | store1 | 70 | | 1 | store3 | 80 | +------------+--------+-------+ 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.
Explanation
select each store and union all.
SQL Solution
# 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