[SQL] 리트코드 1179. Reformat Department Table

문제

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| revenue     | int     |
| month       | varchar |
+-------------+---------+

In SQL,(id, month) is the primary key of this table.
The table has information about the revenue of each department per month.
The month has values in ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"].

Reformat the table such that there is a department id column and a revenue column for each month.
Return the result table in any order.
The result format is in the following example.

 

https://leetcode.com/problems/reformat-department-table/description/

Reformat Department Table - LeetCode

예시

Input:

Department table:

+------+---------+-------+
| id   | revenue | month |
+------+---------+-------+
| 1    | 8000    | Jan   |
| 2    | 9000    | Jan   |
| 3    | 10000   | Feb   |
| 1    | 7000    | Feb   |
| 1    | 6000    | Mar   |
+------+---------+-------+

Output:

+------+-------------+-------------+-------------+-----+-------------+
| id   | Jan_Revenue | Feb_Revenue | Mar_Revenue | ... | Dec_Revenue |
+------+-------------+-------------+-------------+-----+-------------+
| 1    | 8000        | 7000        | 6000        | ... | null        |
| 2    | 9000        | null        | null        | ... | null        |
| 3    | null        | 10000       | null        | ... | null        |
+------+-------------+-------------+-------------+-----+-------------+

The revenue from Apr to Dec is null.
Note that the result table has 13 columns (1 for the department id + 12 for the months).

문제 풀이

SELECT id
    ,SUM(CASE WHEN month = 'Jan' Then revenue ELSE NULL END) AS Jan_Revenue 
    ,SUM(CASE WHEN month = 'Feb' Then revenue ELSE NULL END) AS Feb_Revenue 
    ,SUM(CASE WHEN month = 'Mar' Then revenue ELSE NULL END) AS Mar_Revenue 
    ,SUM(CASE WHEN month = 'Apr' Then revenue ELSE NULL END) AS Apr_Revenue 
    ,SUM(CASE WHEN month = 'May' Then revenue ELSE NULL END) AS May_Revenue 
    ,SUM(CASE WHEN month = 'Jun' Then revenue ELSE NULL END) AS Jun_Revenue 
    ,SUM(CASE WHEN month = 'Jul' Then revenue ELSE NULL END) AS Jul_Revenue 
    ,SUM(CASE WHEN month = 'Aug' Then revenue ELSE NULL END) AS Aug_Revenue 
    ,SUM(CASE WHEN month = 'Sep' Then revenue ELSE NULL END) AS Sep_Revenue 
    ,SUM(CASE WHEN month = 'Oct' Then revenue ELSE NULL END) AS Oct_Revenue 
    ,SUM(CASE WHEN month = 'Nov' Then revenue ELSE NULL END) AS Nov_Revenue 
    ,SUM(CASE WHEN month = 'Dec' Then revenue ELSE NULL END) AS Dec_Revenue 
FROM Department
GROUP BY id

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SQL을 독학하시는 분들에게 도움이 되길 바라며,

혹 더 좋은 방법이 있거나 오류가 있다면 편하게 말씀 부탁드립니다.