LeetCode MySQL-1179. Reformat Department Table

    AllenLi
    LeetCode MySQL

    Write an SQL query to 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.

    寫一個 SQL 查詢來重新格式化列表，像是每個月都有一個部門 id 和一個收入。
可任意排序結果。

    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"].

    Example 1:

    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        |
+------+-------------+-------------+-------------+-----+-------------+
Explanation: 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).

    Solution:
    1. 選擇標題 id。
    2. 將符合 month = [‘Jan’, ‘Feb’, ‘Mar’, ‘Apr’,
    ‘May’, ‘Jun’, ‘Jul’, ‘Aug’,
    ‘Sep’, ‘Oct’, ‘Nov’, ‘Dec’]
    返回加總後的 revenue。
    3. 來自 Department 的 table 。
    4. 以 id 進行排序。

    Code.1 CASE WHEN:

    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;

    Code.2 IF:

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

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