문제
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.
https://leetcode.com/problems/rearrange-products-table/description/
예시
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.
문제 풀이
SELECT
product_id, 'store1' AS store, store1 AS price
FROM
Products
WHERE
store1 IS NOT NULL
UNION ALL
SELECT
product_id, 'store2', store2 AS price
FROM
Products
WHERE
store2 IS NOT NULL
UNION ALL
SELECT
product_id, 'store3', store3 AS price
FROM
Products
WHERE
store3 IS NOT NULL;SQL을 독학하시는 분들에게 도움이 되길 바라며,
혹 더 좋은 방법이 있거나 오류가 있다면 편하게 말씀 부탁드립니다.
