[LeetCode] CASE 테이블 피봇 : 1179. Reformat Department Table

1. 문제

Table: Department

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

(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"].

 

Write an SQL query to reformat the table such that there is a department id column and a revenue column for each month.

The query result format is in the following example:

 

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

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

Note that the result table has 13 columns (1 for the department id + 12 for the months).

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2. 답

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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3. KEY POINT

 

• CASE를 활용한 테이블 피봇 : row 데이터를 colum으로 옮기기 

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leetcode.com/problems/reformat-department-table/

Reformat Department Table - LeetCode