準備月度銷售報告誰擁有最大的銷售客戶，爲下表

Question

準備誰擁有最大的銷售客戶的月度銷售報告，爲下表

Answer 1

這是如何你可以在「一」查詢檢索一個例子：

• 誰擁有最大的銷售客戶的ID
• 該客戶的銷售彙總

首先帶來的CUSTOMER_ID和銷售的相應的總結查詢是這樣的：

select customer_id, sum(sales) as sumsales from mytable group by customer_id; 

這個疑問，等級已被添加到銷售摘要的降序排列。這將允許稍後根據其等級選擇單個記錄。因此，一個包裝是必要的：

select customer_id, sumsales, rank() over (order by sumsales desc) as rnk from 
    (select customer_id, sum(sales) as sumsales from mytable group by customer_id); 

現在的排名條目是可用的，排名第一的記錄，必須選擇：

select customer_id, sumsales from 
    (select customer_id, sumsales, rank() over (order by sumsales desc) as rnk from 
     (select customer_id, sum(sales) as sumsales from mytable group by customer_id) 
    ) 
where rnk=1; 

然而，這未必是實現最有效的方法這個。

編輯：

爲了避免一個包裹層，只是添加的等級，有可能秩foeld添加到第一內部查詢：

select customer_id, sum(sales) as sumsales, rank() over (order by sum(sales) desc) as rnk 
from mytable group by customer_id; 

然後，單個需要包裝的查詢，選擇排名第一的記錄爲：

select customer_id, sumsales from (
    select customer_id, sum(sales) as sumsales, rank() over (order by sum(sales) desc) as rnk 
    from mytable group by customer_id 
) 
where rnk=1; 

參考其他類似的相關答案here。