oj-sql

题目

1795. Rearrange Products Table

列转行思路

1. union
2. 每个select语句内只查一个列

solution

union

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
;