【LeetCode | 数据库】重新格式化部门表

原创于 2025-08-01 14:01:43 发布 · 242 阅读

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题目

表 Department：

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| revenue       | int     |
| month         | varchar |
+---------------+---------+
在 SQL 中，(id, month) 是表的联合主键。
这个表格有关于每个部门每月收入的信息。
月份（month）可以取下列值 ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"]。
 

重新格式化表格，使得 每个月 都有一个部门 id 列和一个收入列。

以 任意顺序 返回结果表。

结果格式如以下示例所示。

 

示例 1：

输入：
Department table:
+------+---------+-------+
| id   | revenue | month |
+------+---------+-------+
| 1    | 8000    | Jan   |
| 2    | 9000    | Jan   |
| 3    | 10000   | Feb   |
| 1    | 7000    | Feb   |
| 1    | 6000    | Mar   |
+------+---------+-------+
输出：
+------+-------------+-------------+-------------+-----+-------------+
| id   | Jan_Revenue | Feb_Revenue | Mar_Revenue | ... | Dec_Revenue |
+------+-------------+-------------+-------------+-----+-------------+
| 1    | 8000        | 7000        | 6000        | ... | null        |
| 2    | 9000        | null        | null        | ... | null        |
| 3    | null        | 10000       | null        | ... | null        |
+------+-------------+-------------+-------------+-----+-------------+
解释：四月到十二月的收入为空。 
请注意，结果表共有 13 列（1 列用于部门 ID，其余 12 列用于各个月份）。

代码

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