Easy之1179.重新格式化部门表

旧城等待， 2022-10-09 04:51 74阅读 0赞

### 部门表 Department： ###

<table> 
 <thead> 
  <tr> 
   <th>Column Name</th> 
   <th>Type</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>id</td> 
   <td>int</td> 
  </tr> 
  <tr> 
   <td>revenue</td> 
   <td>int</td> 
  </tr> 
  <tr> 
   <td>month</td> 
   <td>varchar</td> 
  </tr> 
 </tbody> 
</table>

(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 \[“Jan”,“Feb”,“Mar”,“Apr”,“May”,“Jun”,“Jul”,“Aug”,“Sep”,“Oct”,“Nov”,“Dec”\]。

### 问题 ###

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。

### 示例 ###

Department 表：

<table> 
 <thead> 
  <tr> 
   <th>id</th> 
   <th>revenue</th> 
   <th>month</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td>8000</td> 
   <td>Jan</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td>9000</td> 
   <td>Jan</td> 
  </tr> 
  <tr> 
   <td>3</td> 
   <td>10000</td> 
   <td>Feb</td> 
  </tr> 
  <tr> 
   <td>1</td> 
   <td>7000</td> 
   <td>Feb</td> 
  </tr> 
  <tr> 
   <td>1</td> 
   <td>6000</td> 
   <td>Mar</td> 
  </tr> 
 </tbody> 
</table>

### 结果表： ###

<table> 
 <thead> 
  <tr> 
   <th>id</th> 
   <th>Jan_Revenue</th> 
   <th>Feb_Revenue</th> 
   <th>Mar_Revenue</th> 
   <th>…</th> 
   <th>Dec_Revenue</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td>8000</td> 
   <td>7000</td> 
   <td>6000</td> 
   <td>…</td> 
   <td>null</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td>9000</td> 
   <td>null</td> 
   <td>null</td> 
   <td>…</td> 
   <td>null</td> 
  </tr> 
  <tr> 
   <td>3</td> 
   <td>null</td> 
   <td>10000</td> 
   <td>null</td> 
   <td>…</td> 
   <td>null</td> 
  </tr> 
 </tbody> 
</table>

注意，结果表有 13 列 (1个部门 id 列 + 12个月份的收入列)。

来源：力扣（LeetCode）  
链接：https://leetcode-cn.com/problems/reformat-department-table  
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### 解答 ###

#### 第一步：列拆成行 ####

需要将revenue列根据month拆成行，有两种方式，CASE WHEN或者IF语句。

#### 第二步：行合并 ####

根据题意，需要根据id，将相同id的行进行合并，结果如下表，采用分组的方式，可以对各月收入列求SUM/MAX/MIN/AVG都可以。

#### 法一:Case When ####

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_Revenue
    from department
    group by id

#### 法二：IF ####

select distinct 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 
    order by id;