文章目錄

• • 1. 題目
  • 2. 解題

1. 題目

部門表 Department：

+---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | revenue | int | | month | varchar | +---------------+---------+ (id, month) 是表的聯合主鍵。 這個表格有關于每個部門每月收入的信息。 月份（month）可以取下列值 ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"]。

編寫一個 SQL 查詢來重新格式化表，使得新的表中有一個部門 id 列和一些對應 每個月 的收入（revenue）列。

查詢結果格式如下面的示例所示：

Department 表： +------+---------+-------+ | id | revenue | month | +------+---------+-------+ | 1 | 8000 | Jan | | 2 | 9000 | Jan | | 3 | 10000 | Feb | | 1 | 7000 | Feb | | 1 | 6000 | Mar | +------+---------+-------+查詢得到的結果表： +------+-------------+-------------+-------------+-----+-------------+ | 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，結果表有 13 列 (1個部門 id 列 + 12個月份的收入列)。

來源：力扣（LeetCode）
鏈接：https://leetcode-cn.com/problems/reformat-department-table
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2. 解題

• 按部門id分組，組合 case 月份 when + 求和

# Write your MySQL query statement below 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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