如何選擇第一個值然後忽略休息？

Question

我有數據的表如下：

id activity amount 
1 unknown 20   
2 storage 20   
3 storage 20   
4 swift  20   
5 delivery 50   
6 storage 20   

我想創建一個查詢它帶給我的「計算」之和。 上面..期望的結果的例子是：

id activity amount calculatedsum 
1 unknown 20   0 
2 storage 20   20 
3 storage 20   20 
4 swift  20   20 
5 delivery 50   70   (had 20 and 50 arrived) 
6 storage 20   70 

邏輯是簡單.. 找到的第一行是「存儲裝置」，也就是calculatedsum。當遇到與'送貨'的行添加它，這是新的calculatedsum。

這就是我試圖做的：

select *, 
     sum(case when activity = 'Storage' then amount 
       when activity = 'delivery' then + amount 
       else 0 
      end) over (order by id) 
from A 

但是這不工作...

我怎麼能得到預期的結果？

編輯：id是由創建的列：select row_number() over (order by .... nulls last) as id 該表包含查詢的結果...和eveytime查詢運行表復位它...因此，id始終是實際的行數。

Answer 1

如果您只計算第一個'storage'，那麼您需要確定它。你可以做，使用row_number()：這樣做沒有一個子查詢，如果我們假設爲storage的數額是

select *, 
     sum(case when activity = 'Storage' and seqnum = 1 then amount 
       when activity = 'delivery' then amount 
       else 0 
      end) over (order by id) 
from (select a.*, 
      row_number() over (partition by activity order by id) as seqnum 
     from A a 
    ) a 

一個完全不可思議的方式都是一樣的：

select *, 
     (sum(case when activity = 'delivery' then amount 
       else 0 
      end) over (order by id) + 
     min(case when activity = 'storage' then amount else 0 
      end) over (order by id) 
     ) 
from A a;