[LeetCode]#1179. Reformat Department Table

Environment: MySQL

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).

Solution:

SELECT id,
MAX(CASE WHEN month='Jan' then revenue else null end) Jan_Revenue,
MAX(CASE WHEN month='Feb' then revenue else null end) Feb_Revenue,
MAX(CASE WHEN month='Mar' then revenue else null end) Mar_Revenue,
MAX(CASE WHEN month='Apr' then revenue else null end) Apr_Revenue,
MAX(CASE WHEN month='May' then revenue else null end) May_Revenue,
MAX(CASE WHEN month='Jun' then revenue else null end) Jun_Revenue,
MAX(CASE WHEN month='Jul' then revenue else null end) Jul_Revenue,
MAX(CASE WHEN month='Aug' then revenue else null end) Aug_Revenue,
MAX(CASE WHEN month='Sep' then revenue else null end) Sep_Revenue,
MAX(CASE WHEN month='Oct' then revenue else null end) Oct_Revenue,
MAX(CASE WHEN month='Nov' then revenue else null end) Nov_Revenue,
MAX(CASE WHEN month='Dec' then revenue else null end) Dec_Revenue
From
Department
Group By id

Submitted result:

Reference:

https://leetcode.com/problems/reformat-department-table/discuss/561337/MySQL-Easy-Solution