[LeetCode][MySQL] 1795. Rearrange Products Table

Easy 🔗1795. Rearrange Products Table

📝문제 요약

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.

The result format is in the following example.

Example 1:

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

1단계: store1만 먼저 가져오기

SELECT product_id, 'store1' AS store, store1 AS price
FROM Products
WHERE store1 IS NOT NULL

• 'store1' AS store : 문자열 'store1'을 새로운 열(store)의 값으로 넣음
• store1 AS price : 원래의 가격 값을 price로 바꿔줌
• WHERE store1 IS NOT NULL : 가격이 없는 데이터는 제외

2단계: store2와 store3도 같은 방식으로 작성

SELECT product_id, 'store2' AS store, store2 AS price
FROM Products
WHERE store2 IS NOT NULL

SELECT product_id, 'store3' AS store, store3 AS price
FROM Products
WHERE store3 IS NOT NULL

3단계 : UNION ALL 사용하여 전체 반환

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

💯제출 코드

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