1179. 重新格式化部门表

发表于 更新于

难度系数： 简单

部门表 Department：

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+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| revenue       | int     |
| month         | varchar |
+---------------+---------+
(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"]。

编写一个 SQL 查询来重新格式化表，使得新的表中有一个部门 id 列和一些对应 每个月 的收入（revenue）列。

查询结果格式如下面的示例所示：

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

查询得到的结果表：
+------+-------------+-------------+-------------+-----+-------------+
| id   | Jan_Revenue | Feb_Revenue | Mar_Revenue | ... | Dec_Revenue |
+------+-------------+-------------+-------------+-----+-------------+
| 1    | 8000        | 7000        | 6000        | ... | null        |
| 2    | 9000        | null        | null        | ... | null        |
| 3    | null        | 10000       | null        | ... | null        |
+------+-------------+-------------+-------------+-----+-------------+

注意，结果表有 13 列 (1个部门 id 列 + 12个月份的收入列)。

SQL结构

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Create table If Not Exists Department (id int, revenue int, month varchar(5));
Truncate table Department;
insert into Department (id, revenue, month) values ('1', '8000', 'Jan');
insert into Department (id, revenue, month) values ('2', '9000', 'Jan');
insert into Department (id, revenue, month) values ('3', '10000', 'Feb');
insert into Department (id, revenue, month) values ('1', '7000', 'Feb');
insert into Department (id, revenue, month) values ('1', '6000', 'Mar');

解法：

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SELECT id,
SUM(CASE WHEN month='Jan' THEN revenue END) AS Jan_revenue,
SUM(CASE WHEN month='Feb' THEN revenue END) AS Feb_revenue,
SUM(CASE WHEN month='Mar' THEN revenue END) AS Mar_revenue,
SUM(CASE WHEN month='Apr' THEN revenue END) AS Apr_revenue,
SUM(CASE WHEN month='May' THEN revenue END) AS May_revenue,
SUM(CASE WHEN month='Jun' THEN revenue END) AS Jun_revenue,
SUM(CASE WHEN month='Jul' THEN revenue END) AS Jul_revenue,
SUM(CASE WHEN month='Aug' THEN revenue END) AS Aug_revenue,
SUM(CASE WHEN month='Sep' THEN revenue END) AS Sep_revenue,
SUM(CASE WHEN month='Oct' THEN revenue END) AS Oct_revenue,
SUM(CASE WHEN month='Nov' THEN revenue END) AS Nov_revenue,
SUM(CASE WHEN month='Dec' THEN revenue END) AS Dec_revenue
FROM Department 
GROUP BY id 
ORDER BY id ;

原题链接：https://leetcode.cn/problems/reformat-department-table/