1179. 重新格式化部门表

题目

部门表Department:

Column Name Type
pkid int
revenue int
pkmonth 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:

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)。

题解

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`