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LeetCode 数据库刷题 - 1179. 重新格式化部门表

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发布于: 2021 年 02 月 13 日
LeetCode 数据库刷题 - 1179. 重新格式化部门表

题目:

部门表 Department:

+---------------+---------+

| 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:

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)。

解答: 

-- 行转列问题
# 方法1: 1, 针对id分组; 2, 针对month求和 (使用聚合函数不计算null的特性)select id , sum(case `month` when 'Jan' then revenue else null end) as Jan_Revenue , sum(case `month` when 'Feb' then revenue else null end) as Feb_Revenue , sum(case `month` when 'Mar' then revenue else null end) as Mar_Revenue , sum(case `month` when 'Apr' then revenue else null end) as Apr_Revenue , sum(case `month` when 'May' then revenue else null end) as May_Revenue , sum(case `month` when 'Jun' then revenue else null end) as Jun_Revenue , sum(case `month` when 'Jul' then revenue else null end) as Jul_Revenue , sum(case `month` when 'Aug' then revenue else null end) as Aug_Revenue , sum(case `month` when 'Sep' then revenue else null end) as Sep_Revenue , sum(case `month` when 'Oct' then revenue else null end) as Oct_Revenue , sum(case `month` when 'Nov' then revenue else null end) as Nov_Revenue , sum(case `month` when 'Dec' then revenue else null end) as Dec_Revenuefrom Department group by id
# 方法2: 使用if做判断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_Revenuefrom Department group by id;
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发布于: 2021 年 02 月 13 日阅读数: 13
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LeetCode 数据库刷题 - 1179. 重新格式化部门表