1795. Rearrange Products Table

https://leetcode.com/problems/rearrange-products-table/

Rearrange Products Table - LeetCode

select product_id, 'store1' as store, store1 as price
from Products
where store1 is not null
union
select product_id, 'store2' as store, store2 as price
from Products
where store2 is not null
union
select product_id, 'store3' as store, store3 as price
from Products
where store3 is not null